I RECENTLY CONDUCTED MY OWN SURVEY ON THIS SAME QUESTION. INTERESTING RESULTS.
I recently polled everyone I knew on email about which service they use because I was thinking of switching. I didn't even ask people what they thought of their service... just which one they had. What was interesting to note was that nearly everyone responded back to me with just the name of their service (ie. "Sprint", "AT&T", "Nextel", etc.) except for a few. Overall, there was a pretty even distribution of service among those I surveyed.
Only the people with Verizon responded back with comments like "I have Verizon and I love it!", or "I have Verizon and it's the best!", or "I love my Verizon phone!" It was a very strange distinction. I got to thinking that maybe Verizon puts some sort of digital drugs in their signal to make people so elated about their service, but I realize that their customers are just plain happy with the service.
I have AT&T MLife and it completely SUCKS. I love my phone (Motorola MPX-200), but I HATE the service. I used to have AT&T Digital which I still think is the best. I used to take that phone snowboarding way up in the mountains (East coast, West Coast, Canada) and never a signal problem. MLife sucks bad.