3. Marcelo Bielsa
The currently unemployed Argentine has good experience of the Spanish leagues due to his time in charge at Athletic Bilbao and most importantly brought them a kind of football that was much admired. He got the better of the likes of Sir Alex Ferguson in the Europa League in Bilbao's impressive run to the final which they lost to Atlético Madrid. However he failed to transfer this form to La Liga, with 10th and 12th place finishes in his time at the helm.
Also he has worked with big names before when he was the Argentine manager from 1998-2004. The question is do Barcelona really want to risk choosing someone with relatively little big club experience and also someone who hasn't been successful on two fronts at once.