I'd go for van Gaal, if you want to change the style of the club. He's mad enough, won't stay too long, but I think he's better at changing the basic structure of the club towards a modern approach. Bielsa is certainly more entertaining as a character and even more extreme in his views on the game, but I don't think that could ever work at the top level in club football. And van Gaal actually wants to manage a club in England, is available after the summer and played a part in Barca's and Bayern's development towards their treble winning teams.