I'm a verizon fan because:
1. Their network and customer service have never let me down over 8 years.
2. AT&T's network and customer service was a constant nightmare for for more than 5 years.
3. My employer has always paid my monthly cellphone bill so cost wasn't a factor. If I don't find a job soon, i'll be investigation metroPCS and using my wife's old flip phone.
on a serious note, cost and contracts should be considered. You can get the vzw pre2 for $99 with a two-year contract. MHS is available starting at $20 if you don't use freeTether.
AT&T currently is only viable if you buy an unlocked phone. I don't know if you will have access to AT&T apps such as tethering and gps. But it can be activated without a contract so you are free to move to another carrier if something newer (Pre3, Veer, etc) comes out later this year.
also, you can put your sprint radio into the Pre2 and then continue with Sprint.
there are a few complexities to that, but members such as pastorrich1 actively answers questions about that, and there is even a website link around here for a company that will do the swap for you.
also remember that the GSM Pre2 can be activated on T-Mobile, although I think you will only get 2G data service.