Like someone else said, get it in the 30 day trial period and test it out. If you get good coverage, I would stick with AT&T. As far as a telecom company goes, I have received above average support and customer service from them. I don't feel my bill is too high for what I get ($180 for two iPhones, more minutes than I can count, data & texting, blah blah).
In some metro areas they can still be spotty compared to Verizon customers who will get a better signal, only way to know is to get it and try it or ask a friend near you.
They are quickly upgrading their network though. I lived in Seattle and about 18 months ago their service along parts of the I-5 corridor were awful, by 12 months ago they had added more towers and signal was much better.