the CDMA protocol does NOT go further than a GSM one. This is a common misconception. First, Verizon uses the same long range frequency as AT&T -- the 850 band. Infact they are so close that in order for a repeater to NOT hear both it must be tuned to do so. This said, what makes Verizon seem to go so much further than AT&T is the fact that Verizon will use a higher ACK time and leverage the advantage of using COUNT DIVISION MULTIPLE ACCESS versus TIME devision multiple access, which is what AT&T uses when NOT on 3G. The ACK is what creates an illusion of further coverage, when infact AT&T / Verizon on the same tower, will have nearly identical coverage areas. AT&T however simply cannot have as many associations per sector as a Verizon sector. This is CDMA's advantage.
AT&T's 3G however, should cover basically the same.
On this subject, I can personally say that I'm a big fan of Verizon over AT&T. Verizon seems to not be AS disjointed as AT&T when it comes to handling towers. AT&T doesnt care if a tower stays half functional for over a week at a time. Verizon also uses more intelligent tower placement for coverage of a specific area, where AT&T follows the same rules for extreme rural areas as they do for major cities, thus resulting in 1 tower covering a smaller area. Verizon tends to go to the gusto to get the most out of each site. Its also worth noting, that Verizon does not tend to do NON 360 degree towers. AT*T will do as little as 90 total degrees, even when there is going to be a populated area left uncovered. As for the whole coverage issue, Verizon has about 60% more cell sites than AT&T does, with most of them 3G. I'll agree that in my travels, verizon has been everywhere I've gone in the U.S. -- AT&T / Sprint / T-Mobile just dont compare.