I ride risers in town, but I like drops for longer rides. Rode bullhorns for a little while, and didn't really dig them too much. In the long run, though, just ride whatever is comfortable for you...it's not necessarily going to be the same for you as for others.

Reason I like risers: when I'm riding around town, I often find myself with something in my hand, or adjusting my bag, or something. It's easier (in my opinion) than with drops. Also, as others have said, they're a bit better for getting off and on the bike, getting through traffic and peds, etc.

Reason I (occasionally) like drops: better in headwind, multi-position is better for long rides.

Reason I don't like bullhorns: don't know, just don't feel good to me.