This is relative based on location.
I also have a business phone with Verizon and I have absolute minimal reception with Verizon at my house with calls dropped often. I don't have full reception with AT&T at my house, but much better than with Verizon, which is the same at a number of places that I frequent most.
Verizon certainly has better coverage than AT&T in certain areas and AT&T has better coverage than Verizon in certain areas. No major provider in the U.S. has excellent coverage everywhere.
AT&T did not become the largest in the U.S. by number of subscribers completely by accident.
In the early going, Apple initially approached Verizon about being the provider for the iPhone in the U.S., but Verizon wasn't willing to meet Apple's demands. AT&T, Cingular at the time, was willing.
GSM networks also dominate the overall worldwide market by a very significant margin. Had Apple gone CDMA with the iPhone, the number of countries where the iPhone is currently available and the number of coming soon countries would be significantly smaller.
It looks like Verizon will be going with an LTE network in the not too distant future - which will be 4G. They will have their work cut out for them with the transition from their CDMA network to LTE with both networks having to run side by side for a long period of time while their LTE is being built out, and at some point CDMA network access being turned off. But this will add/include Verizon's network with the worldwide standard and make the iPhone at that time compatible with their network. This may not resolve what prevented Verizon from agreeing to Apple's demands for the iPhone, but things may be different in this regard in 3-5 years.