Some other differences are that GSM device (Cingular and Tmobile) use sim cards to store your account/network information (and contacts if you choose), which can easily be switched out between phones.
I use Verizon, mainly because I've been a customer for so long, and they have a great network, and I don't travel internationally (at least not currently or in the near future)
Here's a pretty
detailed comparison chart from Treonauts.
It may help shed some further light.