Obama's style is pretty dead serious. You would want someone who is good with humor but won't be a big risk of making a fool of him/herself. Huckabee would be a good debater, as would Pawlenty or Gingrich most likely. Romney is also dead serious in tone, which would hurt him. Daniels also seems to be a little too serious. Palin would probably end up mixing up California and Florida or something similar.
I think Thune, Santorum, Huckabee, Romney and Gingrich would all be strong debaters. Especially the last three.
I think Romney would do a good job, don't get me wrong, but I think his style is very similar to Obama's so someone like Huckabee or Gingrich or Thune might be more effective because they all have that "folksy" side.
