I prefer IPB rather than phpBB. Althouth we will have to wait and see what phpBB3 is able to do and in what way is it improved. The biggest problem IPB has is the fact that v2 is not free... So that's one point for phpBB.
Refering to mods and skins, skins are much better IPB ones, at least ExtremePixels skins, but talking about mods, both of them have nearly the same. I wouldn't even consider SMF.