In general (all things equal like tower location and signal strength) GSM is better for data and CDMA is better for calls. Most iPhone 4 test have also concluded this.
Personally, I'm getting a 32GB w/ ATT 3G. Since I currently have a Verizon iPhone I can use MiWi if I would like or activate the 3G if traveling and/or care about draining my iPhone's battery. In my opinion it is the best of both worlds.
My question is what sort of data speeds are people seeing with their VZW iPhones? I get great local AT&T coverage and speed here in KC, but the reason I am thinking of VZW is the 3 or 4 times I travel back to my parents house VZW has much better coverage. I can use the Wifi hotspot locally but thinking VZW would be better in the long run.
I haven't used VZW 3G in nearly 4 years... any speed results out there?
You sorta answered your own question. If you are unhappy with AT&T service on your iPad 1, chances are you will be unhappy with it on iPad 2.
I am not saying Verizon would be a better option. It is conceivable that Verizon and AT&T coverage in your area are both equally crappy. Check and double check coverage maps and ask other users in your area and go from there.