service wise verizon is the best,but most of the verizon phones you cant unlock in the future to use a different service since its a CDMA system that works with the radio system on the other side att service is not bad either but the phones can be unlock in the future if you break a contract or sumthing.
Pricing probably won't be too different. Verizon usually gets rated best (or close to it) for coverage, reliability, and customer service - whereas AT&T usually gets rated at the bottom or close to it.