It's the one I run, but that's because I consider it to be the least eye-hurting (I have no vision problems or anything of the kind, but if I have a choice, I go for the one easiest on the eyes). White text on a dark background is generally my preferred way of viewing forums.
Same here.
The Eeveelutions, Charizard, Mewtwo, and Lucario are popular.
I've seen quite a few Roserade and Honchkrow in user's Sigs/Avatars/etc. lately, too...Same goes for Rotom and his/her Formes, and Shaymin Sky Forme (I haven't seen as many Land Forme Shaymin, though. Poor hedgehog).