My fiancee and I recently switched from Verizon to AT&T after Verizon royally pissed us off (repeatedly gave us problematic phone replacements; my boss was getting pissed).
A few things I've noticed:
- Verizon does have better / more service in general, HOWEVER, when there's no (or ridiculously low) service on Verizon, it usually displays one or zero bars rather than "No Service." It will lag when trying to make a call, but generally won't notify you that you simply have no service. AT&T, on the other hand, will simply display "No Service."
- AT&T's 3G speeds are roughly 1.5 to 2 times faster than Verizon's in most areas. It still comes down to who has more bars in a given area (if AT&T only has 1 bar / 3G in an area and Verizon has 4 bars / 3G, Verizon will usually be faster), but I've found AT&T to have the upper hand in most areas. Provided, I was comparing my Verizon Droid X to my AT&T Atrix.
- If tethering is what you care about most, AT&T seems to be the better deal. I'm paying $25 / 2GB of mobile data, plus $20 for another 2GB of tethering data. $45 total, and the entire 4GB can be used for tethering. On the other hand, Verizon was $30 for "unlimited" (~5GB) of mobile data, plus $20 for 2GB of tethering data. $50 total, only 2GB for tethering.