I've only used Verizon, but from my experience with them, if they are as good as people claim, I may as well stop using Cell Phones.
As for my phones themselves, I had a terrible Keyocera that I don't even want to talk about, and I know have a Samsung SCH a890. It's a really good phone. Bright backlight, nice volume, has V-Cast functionality, the web browser is easy to use, the keypad is easy to read, the camera has nice features (including an actual flash that works fairly well).
Only complaints are the restrictions on voice recording (only up to a minute; not very handy for recording speeches, etc. at debate tournaments, but good for memo type stuff), lack of bluetooth (which means no way to connect it to my computer), and battery life. This thing was one of the first to have V-Cast functionality, so obviously the battery life isn't that great.