I see most of the US posters are in the northern states... that's gotta make a difference!

For MTB I prefer 1/2 finger gloves for a few reasons:
1. they are cooler on hot days.
2. my stubby fingers don't fit well in most FF gloves.
3. I like to be able to feel the levers and I don't like the subtle sliding of material between my fingers and levers.

To each, his/her own!