As far as watch-style computers go, I like my D6 (the original, non AI). I chose a watch style over a larger wrist style because I like to have my computer with me at all times. If I know where it is, I won't lose it. I also like not having to switch what's on my wrist between a computer and a watch. I don't have to leave a watch in the hotel room while I'm out diving, or leave the computer in the hotel room when I'm out doing something else, so there's less chance of them being lost or stolen. It's always on my wrist. I also like to be able to review logged dives when the day is done and my buddies and I are sitting around the bar, discussing what we did, and entering dives into our logbooks. Inevitably, someone with a non-wristwatch computer will stand up and say "I need to go get my computer from the room." In summary, I find the wristwatch style conducive to a certain style of diving.
That said, at some point in the future I will probably switch to something like a Shearwater. For some styles of diving, the advantages will outweigh the inconveniences noted above. Moreover, the screen on my D6 looks smaller every year. I don't think my eyesight will allow me to continue using a wristwatch-style computer for many more years.