I don't really care for tauren paladins at all, their lore seems so out of nowhere and I'd much rather have Forsaken as the new Horde paladin class. If they can be priests then I don't see how they can not be paladins.
Goblin shamans look pretty stupid despite having their in-game relationship with elementals explained (there's this goblin in Deepholme shown doing business with his elementals). They haven't shown to ever care for any shamanistic stuff and I don't buy that they can become so skilled, to the point that they get to be the so-called class leader and gaining Doomhammer.
Forsaken death knight, because of how silly their backstory looks now. So first they were a normal human in Lordaeron, died by Arthas and were raised as an undead, broke free and joined Sylvanas, died again and serves Arthas again, broke free and serves Sylvanas again, dies yet again during the Arthas fight and almost had to serve Arthas yet again... Forsaken DK's are literally frisbees being played by Arthas and Sylvanas.
Pretty much every monk except pandaren, actually I could see humans being monks as they were trained so in Scarlet Monastery. Forsaken monks look the most stupid as their limbs should break off the moment they kick or punch. It also doesn't make much sense that a gnome can hit just as hard as a tauren.
Not saying they should all be removed but I find them the most dumb combo's.