I think it all depends on your specific location. I know that in my area I am getting a consistently good signal, much better than I ever got on my Verizon BB. In fact, people have said that I sound much better on the iPhone than I did on the BB.
I did have the "o" incident today, but it went back to 3G pretty quickly.
Where I live, which is northern NJ, Verizon has the best signal of all the carriers; I don't know anyone who isn't on Verizon. Around here, Verizon does have the most reliable network.
As you said, YMMV, and that really depends on where you live and/or spend the most time. It's less carrier vs carrier as it is location vs location, at least IMHO.