Neither. I would go with Verizon Wireless and if you are currently on Verizon Wireless why is the world would you switch. They have the best coverage and some awesome devices. Check with your local store or call 1.800.2JOIN.IN to see what they can offer you.
I have had AT&T since before it was AT&T (back when it was still Cingular) and i have never been disappointed with their service. Always have full bars and vary rarely drop calls...so yes, i say it is a good provider.