I prefer no body in first person personally because it doesn't add anything for me. It somehow only makes games less immersive to me usually, although I can't explain why.
It's because the game do the job of your imagination, and usually, it does it bad.
Except mirror's edge, all the game where I could see my legs disappointed me, because of the animations.
Take Oblivion for example, when the 1st person body mod appeared, I downloaded it right away. Then I played...
It just didn't felt good at all. When I was climbing a mountain, I use to imagine my character, well, actually climb. I could pictures his hands grabbing rocks, his feet finding good places etc.
When I could see my legs, it was just the standard walking animation working. That just looked horrible.
What was meant to emphasize immersion actually broke it totally.
So if I see my legs, i hope for REALLY credible animations. If not, please let my imagination do the work.