I'm currently leveling one, and I think I might choose it for my mage in the future as well.
Might change once new character models come out. Currently I like the way my favorite paladin sets look on belfs better than they do on tauren, but that might change. I only play female characters btw.
For me belfs are like the humans of the horde, boring and easy to pick so I try to make as few as possible and rather branch out to other races. However I'd like to have at last one belf whereas with humans I'd prefer to have none.
I have 4 lvl 90 pandas though :3 the pandaiest panda