Not being an AT&T defender. I am not happy with their service since I switched for the iPhone 4 and I plan on going back to verizon eventually.
However, this doesnt prove anything. AT&T had the first iPhone in 2007. Around 3 years after verizon got their first iPhone. and AT&T has 2/3rds of the iPhone 4's out there, not to mention the 3GS and 3G on their network as well.
For the most part, AT&T has been fine. I have found 1 dead spot in Scottsdale and 3-5 total dropped calls over the year plus that I have owned an iPhone 4. It all changed when I traveled to certain cities. In San Francisco the network was utterly useless downtown. Same thing happened when I was in Las Vegas. Also at most major sporting events. Anywhere there is a massive amount of people the AT&T network gets just destroyed.