I like Verizon they have the best coverage in my area. The others don't cover much outside the major cities so you are roaming more often if you go out in the country for a drive. I have been with them 7 years and no problems at all. Also I have a data plan and only AT&T and Verizon really offer them.
As far as total numbers of phones I have no idea who has more. I know I walked in the Verizon store and saw at least 50 why I would need more than that to choose from I am not sure.
I have the new slider phone.