Human for alliance and Undead for horde are my favorite. I recently did troll and it was pretty annoying. BE is the worst in my opinion, lots of collection quests and they haven't modified them for group looting yet so back to the old days of doing collection quests 4-5 times. With RAF I just go to the dead scar with all the skellies and farm them until level 10 then gtfo.

Orc is ok, but some not so boxing friendly quests. Tauren is... well that zone is huge and spread out, and running around sucks.