Martinez is a good coach and has done well with Belgium, I think he would have us playing exciting football but not sure it would be winning football in Europe at least. He is Catalan also, so will understand what the club means and how important the style is and If he brought Henry with him then that would provide a link to the players.
Don't want Alegri, the football Juve plays is not compatible with Barca.
Blanc would be interesting, I thought he would make a top class manager when he was at Bordeaux but it hasn't worked out for him, though he did well at PSG, I would be ok with him getting the job.
Koeman hasn't really impressed in club football as a coach but has done well with the Netherlands so far, but I do think he would be true to Barca's philosophy and he is a big character that won't be dominated by the players.
Poch would be first choice and I know he has said he would never coach Barca, but if the job was there for him would he really turn it down? I don't think so, you can't pick and choose like that. Great City, Great Salary, Great Players, Great Stadium and Resources and he would turn that down because he played for Espanyol? I don't think he would.