I have a first gen iPone, and a Blackberry Bold. Both on At&T.
I also have an HTC Diamond I used to run on T-Mobile, but is just sitting there right now.
I like the iPhone the best. Just works for me. I find the Blackberry Bold’s menu’s unintuitive, the trackball is very odd feeling and I always move when I try to click, the web browser is horrible, the music player seems dated, and the solitaire game is horrible.