I've had zero problems with coverage or speed with my iPad1 on AT&T. In the past year my travels have taken me to Denver, Albuquerque, St George UT, Sacramento and San Diego CA on the west coast, and NYC, Boston, Pittsburgh and Atlanta on the east coast. All of these trips have involved driving around and being in different parts of those towns. Add airport layovers in Phoenix, Houston and a divert to Memphis for an hour. Then tie in my near daily around town use here in Las Vegas. AT&T has been good for me.
If I could knock them for anything at all it's that their Las Vegas Strip capacity is lacking during major events. When the strip area is full, they slow down.
So when I get my iPad2 tomorrow, it's an AT&T unit. I'll give them another year. Thats the beauty of the no-contract setup. If by iPad3 Verizon is kicking their ass in speed I'll jump ship happily, assuming they'll match my unlimited plan and pricing.