#3 Marcelo Bielsa

Marcelo Bielsa is another manager Barcelona could have appointed instead of Ronald Koeman.
Bielsa has done a commendable job at Leeds United since being appointed their manager ahead of the 2018-19 campaign. The Argentine led the Peacocks to the Premier League just two years after his appointment. He has managed to keep them in the English top flight for the last two seasons.
The tactician plays an attacking brand of football that is beautiful to watch and effective as well. His team shocked the Premier League last season when they beat champions Manchester City 2-1 at the Etihad Stadium. They also earned decent results against Chelsea and Liverpool.
Marcelo Bielsa is a huge admirer of Barcelona. Had the Blaugrana made an approach to secure his services, he would've likely chosen to join them. His style of play apparently suits the Blaugrana's system more than Ronald Koeman's.
#2 Erik Ten Hag

Many expected Barcelona to make a move for Ajax manager Erik Ten Hag when they relieved Quique Setien of his duties ahead of last season. Surprisingly, the Blaugrana opted to appoint Ronald Koeman, who hasn't really justified his appointment.
From many indications, Erik Ten Hag was probably the best option for the Blaugrana. The Dutchman shares the same core principles as Barcelona. He plays attacking football with emphasis on possession, pressing and composure.
The tactician also knows how to get the best out of young talents. His young Ajax side shocked the football world when they defeated Real Madrid and Juventus to reach the Champions League semi-finals in 2018-19.
#1 Luis Enrique

Luis Enrique needs no introduction. The Spaniard was in charge of Barcelona during one of the most successful periods in the club's history. He guided the Blaugrana to the top of European football, and made a huge statement in the league as well.
Barcelona were a huge force to be reckoned with under Luis Enrique. The Blaugrana struck fear into opposition teams with a forward line of Lionel Messi, Neymar and Luis Suarez.
The tactician delivered a historic quintuple during the 2014-15 campaign, winning the Champions League, La Liga, Copa del Rey, UEFA Super Cup and the Club World Cup.
He led Barcelona to ten trophies during his three-year spell at Camp Nou, making him one of the most successful managers in the club's history. It would've made sense to turn to the Spaniard instead of Koeman.