just my .02 here......
if i had to make a choice i would look at the service providers. now that verizon & alltel have merged and have much better towers in my opinion, i think that i'll stick with big red for a long time. i don't care too much for companies that try to dominate the market just becasue they have a hot product.
no doubt that the iphone is a very good phone, but i've seen it way too many times when friends of mine lose their service signal and they're right next to the tower. i'll just say, "here... use mine"
pdub73 hit it on the head.... each one has it's issues. do your research, and i would take advantage of the 15 day trial period that each company has to offer.