While many have swapped Arsenal for Barcelona, not all of the moves have turned out for the best, both players and the clubs alike, With 9 players transferred between the clubs since the turn of century, we look at the real winner of these moves between the 2 clubs.

Alexis Sanchez (Euro 42.5 million)

Barcelona (2011-14)
Joining Barcelona in 2011 for Euro26 million fee from Udinese, Sánchez became the first Chilean to play for the club. Capable of playing anywhere across the front three of the Barcelona system, Sanchez was always going to be in the shadow of Messi and David Villa at Barcelona. Replacing Zlatan in the line-up was always going to be big shoes to fill, but the talent and tenacity was obvious.
Won 1 La Liga title and Copa Del ray with the Catalans
Arsenal(2014 - )
On 10 July 2014, Sánchez signed for Arsenal, becoming the 2nd marquee signing in consecutive seasons after Mesut Ozil in 2013. Sanchez helped Arsenal retain the FA Cup in his first season and made the Gunners faithful excited about his talent. It was obvious that the team will be built around him for seasons to come. His goal against Aston Villa in the final is a collector's item. He capped off his first season by winning Arsenal's Player of the Year award. During the second season at the club he helped Arsenal finish 2nd to surprise runners-up to Leicester City.
Sanchez has now taken on the "No 7" jersey signaling him as the main man for the team ("as if that needed any further re-inforcement"). The 2017 season has also seen him operate in a more central role and being preferred over Giroud as the main strike option. Currently, he is the leading goal- scorer in the premier league and looks determined to take the Golden Boot.

Winner : Arsenal , Arsenal 1 – 0 Barcelona
Sanchez is definitely playing the best football of his life at the Emirates and now it is hard to imagine life without him for Arsenal.

Thomas Vermaelen (Euro19 million)

Arsenal (2009-14)
Vermaelen joined Arsenal from Ajax for Euro10 million (rising to Euro12 million) in 2009, replacing Kolo Toure at the heart of defence and partnering with William Gallas, Affectionately called the "Verminator" During 2009-10 season Vermaelen became notable for being a goal-scoring defender due to his spectacular 25-yard, left-footed goal against Blackburn Rovers and his many headed goals. He was nominated for the Belgian Sportsman Of The Year award and was also included in the PFA Team of the Season. Vermaelen became the vice captain with the departure of Fabregas to Barcelona. In August 2012, Vermaelen was announced as Arsenal's new captain, replacing Robin van Persie upon his departure to Manchester United. On 17 May 2014, Vermaelen won his only trophy with Arsenal , the 2014 FA Cup Final although he was an unused substitute in the finals.
Barcelona (2014- )
In 2014, Vermaelen moved to Barcelona for Euro19 million. Vermaelen has been plagued with injuries since his transfer. Making no significant contributions and currently out on loan at Roma.

Winner : Arsenal , Arsenal 2 – 0 Barcelona
Getting 19million for squad player is decent money, with the track record of injuries he doesn't seem to be making any headway at Nou Camp and his best years are definitely behind him.

Alex Song (Euro 19 million)

Arsenal (2006-12)
Although at the club since 2006, 2008-09 was the breakthrough year for Song producing some eye-catching performances and emerging as a genuine mid-field option for the Gunners, this continued till the departure of Fabregas in 201, when he took on the responsibilities of providing assists for Van Persie (the cheeky over the top ball at Everton during the 125th anniversary game for Van Persie to smash in and the assist for Henry in FA Cup against Leeds) He was voted in second place as the Arsenal player of the season by the fans in 2012.
Barcelona (2012-16)
As had become the norm, Barcelona again came calling for an Arsenal midfielder and Song followed in footsteps of Hleb, Fabregas etc etc to the streets of Rambles for a 19 million transfer fee. After an initial stop and go period at Nou Camp loan spells at West Ham followed for Song, (come on he really did not have a chance in the midfield of Iniesta, Busquets, Rakitic and Fabregas). After, some strong displays at East London club. Barcalona let him go to Russia on a free.

Winner : Arsenal , Arsenal 3 – 0 Barcelona
Song provided Arsenal with continuity after Fabregas' transfer and steadied the ship for them, his spell at Barcelona had nothing of note to remember.

Fabregas (Euro 34 million)

Arsenal (2003-11)
 Fàbregas joined Arsenal's Academy in September 2003. In October 2003, he became Arsenal's youngest-ever first team player, aged 16 years and 177 days in a League Cup tie at home to Rotherham United. He then became the youngest goalscorer in Arsenal's history in a later round of the League Cup. Although, technically a part of the "Invincibles Squad" he was not awarded a winner's medal because he did not play a single league game.
The injuries and subsequent departure of Vieira helped Fàbregas cement a position for himself in the center of the park for Arsenal, in the process also becoming youngest goal-scorer for Arsenal in a League game. He cemented his Arsenal legend by throwing a pizza at Sir Alex in "Battle of the Buffet". The departure of Thierry Henry at start of 2007-08 (who also signed for Barcelona), Cesc became the most important player for Arsenal. He was appointed the club captain during the 2008-09 season. The captaincy had a positive effect on the Spaniard and he became the go-to man constantly chalking up assists and important goals for the team. (the goal at San Siro and the solo run goal against Tottenham are unforgettable)
Obviously, the performances on pitch caught the world's eye and the infamous Barcelona jersey on Fabregas incident post Spain's world cup celebrations put the final touches to his imminent departure to his boyhood club.
Fabregas' time at Arsenal is fondly remembered (i.e till his move to Chelsea). But he could only get his hands on 1 FA Cup, and lost in 3 finals with the Gunners.
Barcelona (2011-14)
On 15 August 2011, Barcelona signed Fàbregas. He had a good tally of goals and assists for the club, but was never the main man which he was at Arsenal, although that was never going to be with the likes of Messi, Villa and Iniesta in the team.
Fabregas' time at Barcelona ended with a feeling of what could have been. But he got the success which eluded him at Arsenal, his time at Barcelona had 1 La Liga, 1 Copa del Rey, 2 Supercopa de España, 1 UEFA Super Cup and the 1 FIFA Club World Cup to show for his troubles.

Winner : Arsenal , Arsenal 3 – 1 Barcelona
With Fabregas moving to Barcelona, Arsenal certainly missed the midfield maestros best years. Although, he never hit the heights expected of him at Barcelona he did win multiple trophies with the Catalan giants.

Hleb (Euro 17 million)

Arsenal (2005-08)
In June 2005, Hleb joined Arsenal, Hleb quickly established himself as a first choice player and his technical prowess was very visible. Hleb was always a popular figure at Arsenal, and the fans reciprocated the effort he brought to the team by inventing a song to the tune of Johnnie Allan's Rubber Dolly, "Alexander Hleb, Alexander Hleb, He's good at football, Alexander Hleb. His partnership with Fabregas was a delight for the Gunners faithful.
Barcelona (2008-12)
In July 2008, Hleb joined Barcelona, by March of next year it was clear that he was signed to be a squad player rather than for the first team. Hleb openly admitted to wanting to move away to utilize his best years in football towards the end of 2008-09 season (Barcelona won the treble in that season, with Hleb playing no real part in it). He returned to his earlier club Stuttgart
In July 2009, Hleb returned to VfB Stuttgart on a year loan deal and then to Birmingham the next year and to Stuttgart again the next year, briefly he expressed his desire to return to Arsenal after his spell at Birmingham (but we all know you don't really get to come back to Arsenal unless you have already scored 226 goals for them, sadly in Hleb's case he was only 216 short). He never returned to the club and left shortly after

Winner : Arsenal , Arsenal 4 – 1 Barcelona
Hleb could may have become a world class player had he stayed on with Arsenal but his move to Barcelona didn't take him to the heights expected of him.

Thierry Henry (Euro 24 million)

Arsenal (1999–2007)
Henry transferred to Arsenal in 1999 reuniting with his former manager Arsène Wenger who moulded him from a winger to a world class forward. The statue outside the Emirates is a testament to his contribution to the North London Club. He gave countless world class goals to the Gooners to remember (turn and shoot over Barthez, solo run goal at the Bernebau and the list goes on……).
During his time at Arsenal, he was named the PFA Player' Player Of the year twice, the FWA Footballer of The year three times, for 2 continuous years in Henry was runner-up for the FIFA World Player of the year. With the team, he won two league titles and 3 FA Cups at the club. Henry spent his final two seasons with Arsenal as club captain and lead them to the 2006 UEFA Champions League Final.
We can go on about his time at Arsenal, but in simple words the man is an Arsenal Legend
Barcelona (2007-10)
In June 2007, after eight years with Arsenal, to fulfill his personal ambition of winning the Champions League he moved to Barcelona. In 2 years time, he fulfilled the dream and was an integral part of the club's historic treble winning side when they won LA Liga, the Copa Del Ray and the UEFA Champions League, and went onto achieve an sextuple by also winning the Supercopa de Espana, the UEFA Super Cup, and the FIFA Club World Cup. He moved onto New York Red Bulls signaling the end of his career in Europe.

Winner : Thierry Henry , Arsenal 5 –2 Barcelona
To pick a winner would be unfair, the statue outside the Emirates which speaks volumes about his contribution to the North London club. Arsenal would have preferred for him to retire at Arsenal but personal ambition drove him to Barcelona and he was able to achieve the success he set out to. A happy story (minus the tearful parting message to Gooners) and everyone was a winner.

Giovani Van Bronkhorst (Free)

Arsenal (2001-04)
Van Bronckhorst was signed to replace the midfield void left by the departure of Emmanuel Petit, however his period at Arsenal was marked with injuries and made only 64 appearances over the course of 3 seasons.
Barcelona (2004-07)
Moving to Barcelona on a one-year loan and then on a permanent transfer, he quickly established himself as the right-back in Frank Rijkaard's team. Produced some fine displays in the Barcelona shirt and won the La Liga title and the Champions League title as well (ironically against Arsenal, which was Gunner's only appearance in a Champions League final)

Winner :Barcelona, Arsenal 5 –3 Barcelona
Barcelona were able to extract the kind of football from Van Bronkhorst that Arsenal signed him for, his greatest moments and finest displays came in the Barcelona shirt and many Gooners would already have forgotten that he ever played for the North London side.

Marc Overmars (Euro 40 millions)

Arsenal (1997-2000)
Signed for Arsenal in June 1997 along with Petit, he brought some of the initial expansive football which Arsenal is now recognized for. Always exciting with his wing play and pacey runs, he helped Arsenal to a double in his first season with the FA Cup and League title win. He scored the infamous winning goal against Sheffield United in the FA Cup when Kanu failed to return the ball to the opposition for injured player to get treatment. Helping the team to the 2000 league title, he moved onto Barcelona for a record fee for a Dutch footballer.
Barcelona (2000-04)
His Barcelona career got to a slow start, but Overmars made place in the team by the end of first season which the Catalans finished in the fourth position but media touted him as the only decent player in the Barcelona team. The team finished at the same position the year after too. Compared to the previous season, Overmars started being used more sparingly in matches, but made a difference whenever he was thrown into the action. But injuries continued to hamper him through his time and a persistent knee injury forced him to announce his retirement from football in July 2004 and left Barcelona without compensation.

Winner : Arsenal, Arsenal 6 –3 Barcelona
Considering the sizable chunk of transfer fee involved, Barcelona were never really able to get their money's worth. Arsenal moved onto greener pastures with Pires and Ljungberg and the best years of Arsenal under Wenger followed.

Emmanuel Petit (Euro 15 million)
Arsenal (1997-2000)
Joined Arsenal in June 1997, his partnership with Vieira was the cornerstone on which the Gunners build their success. A double ensued in his first season with the FA Cup and League title win. After 3 successful years at Arsenal he moved to Barcelona
Barcelona (2000-01)
When your coach doesn't know which position you play him, you are bound to underperform, a situation which happened with Petit at Barcelona. A move after one year beckoned him back to the Premier League with rivals Chelsea.

Winner : Arsenal, Arsenal 7 –3 Barcelona
Petit certainly contributed a lot more to Arsenal than he did to Barcelona, transfer back to the Premier League only after one season in Spain was a testimony to the same.

Barcelona have paid a cool 32% of the cost of building the Emirates back to Arsenal, with Arsenal having pocketed a cool Euro 125 million (net) from transfer dealings with Barcelona. Arsenal seem to certainly have Barcelona's number when it comes to getting the better bargains and the best of the players of their time at the 2 clubs. But, without doubt the transfer of a number of marquee players to Barcelona has been disruptive to the progress of Arsenal, the real cost of which can never really be truly calculated.