I'm glad they stuck with ATT.
Where I have lived and traveled over the past 3 years (length of iphone ownership) in the midwest, ATT has always been good.
I lived in minneapolis, ALWAYS 5 bars.
I live in Chicago, great coverage and much faster data than verizon.
Traveling to cleveland, orlando, lansing, milwaukee, coverage has always been good.
I can't speak for the coasts but I'm glad I have ATT. Verizon's 3g coverage in chicago is crap and their speeds are much lower. A very good friend who has an incredible routinely participates in speed test comparisons with me while we're out and about. ATT is the clear winner in Chicago, and its not even close.
Just the other night I hit 572 kilobytes/second down. Thats about 4.5 Megabit. And with a constant 1.5 MBit uplink, I'm uber-happy.
A fandroid with an EVO recently did a speed test comparison with me while we were at the same place, and he had "4G" coverage. He got 2.5 megabit and I got about 3.
"4G" is a ridiculous marketing technique. Its hardly in ANY major cities, but chicago happens to be one of them and it can't even keep up with ATT 3G.
Nuff said.
I can't find the exact test result I was talking about but heres a similar one so everyone knows I'm not just full of hot air:
http://www.speedtest.net/iphone/42835179.png