I assume you're asking about the best Marvel PFs. In that case, Doom is the best, although the Hulk and GG are close. Cap may even beat Doom, but we'll have to see the final product first.
Although I only have Punisher (bought 2 days ago and still in shipping process though ) I voted for green goblin. I found him the best representation of the character so far.
Well compared to Doom, the Hulk is pretty "plain." Don't get me wrong, I think the Hulk is a fabulous piece, but the detail on Doom just can't be beat. I think the Green Goblin comes very close though.