I really don't understand the answers that have been given whatsoever.  Regardless, my opinion is that Gnome and Troll Protection warriors are the worst PvP class/race combo, followed distantly by all protection paladins and other protection warriors.  Those are mostly PvE specs, and have little use in PvP (although diving into the middle of an epic battle and using Shield Wall in AV is very fun).  Tauren marksman hunter, Gnome CM rogue, and Human Shadow Priest are also some crappy combinations, IMHO.