I've had Verizon for like two years, and it's worked great for me. I have a share-talk plan with my mom. It's not nationwide, but I live right on the border of Iowa and Illinois, so Chicago is included in my plan, as well as Iowa City, so when I went up to Chicago this summer, my friend couldn't even use her SunCom, and I was able to, and it wasn't roaming. We've never had any problems with Verizon, except this summer my mom couldn't dial out or recieve calls, and we went to the store and they had to enter the authorization over, because they had been working on the network, but they addressed her concerns and fixed her problem in like five minutes, so the customer service reps were great.
My friends all have SunCom, and the network is rather small, and also my friend was "hotlined" by them like three times, and they shut her phone off, claiming that her bill was past due... and it never had been.
The only thing I don't like is my phone is like 3 years old (It's an LG 330W) and they don't sell it in the store anymore, so I can't get a new battery unless I order it online, and the phone thinks it's roaming when it's not, so the caller ID doesn't work when the phone thinks it's roaming (when I'm in Iowa City), because it thinks it's out of area. Weird, but it's not Verizon because it worked when I went to Chicago...
I really want a new phone, but it has to be a flip phone because I don't like talking on flat ones, also I will not purchase a Nokia phone. All of my friends have had problems with them, and the service wasn't great, and I'm just not impressed with what features they have--come on games--I think that's silly to drain your battery on games on a cellular phone, but that is just me.
Anyway, enough of my blathering... good luck on finding a phone.