Both alliance and horde has great choices. Here is my casual favorites
(New models)
1. Tauren (male) - Because it feels good to smack around when everyone around you is a small shits.
2. Orc (male) - Special is little turn off, but nobody can beat orc for his new animations, hes a totall badass
3. Human (male) - Really nice special swing, and great mogs, overall I think he is amazing as orc
4. Belf (male) - Love that chest out hero attitude, looks good in gear, but taunting graphics is a really big switch off, can be to jumpy sometimes.
5. Belf (female) - Little bit stiff on some moves (block, stomp), but It can be fun, (for paladin tank female is number one choice)
6. Troll (male) - Quite intimidating, swift moves, especially taunt animation is my favorite.
7. Dranei (both) - Not the biggest fan, but they can be fun.
With new models, nelfs are quite turn off to play, forsaken is a joke, and things like dwarf, goblin, gnome (even overall gnome new graphics are nice) and worgen I wouldn't consider (with old models I would include forsaken and nelfs both male and female)