Favorites for the Barce job are two Argentines.. one Gerardo "El Tato" Martinez, he guided Paraguay to a Copa America final in 2011 and also guided them to the 2010 World Cup Quarters iirc.. He is currently the coach of Newells Old Boys in Argentina, which is Messi's old club when he was a boy, he actually lead Newells to the Semis of the Copa Libertadores but fell in Penalty Shoot-out to Atletico Mineiro.
The other is El Loco Bielsa.. a very meticulous headcoach, whose also very hardheaded and aggressive in his headcoaching approach. When he took over Athletic Bilbao he asked for the tapes of every Athletic Bilbao game from the season prior.. and for like a week or so he saw each game TWICE. That same season he led Athletico to a midtable finish but to two finals, a Europa League Finals where they fell to Falcao and Atletico Madrid and the Copa Del Rey final where they fell to none other than Barce.