That is an interesting point about monster chopper. His defense absolutely must be above the big 3. Only judging by how the rest of the crew had to stay away from such attacks, where as Chopper just stood there. Granted he was fighting a technicly weaker apponent, but this is One Piece, and someone like Usopp can stand up to Luffy at least for a while.
As far as the one hit thing with no "special ability" that is also interesting to note. The way he hit Kamudori(sp?) was devestating, and just super over powered. It seems like it had almost the same affect as Luffy's Giant punch against Lucci when he used Tekkai. But Lucci just about passed out, and didn't Kamudori get up after a hit like that?
Wow, im inclined to think that Monster Chopper is on par with Giganto Luffy attacks. But because he can't think straight that puts him way below the top 3 IMO.