I think, based upon all the cell phone service providers that I've had, that I can accurately compare the above services with each other. First, I had TracFone...
I got a TracFone when I was 12, maybe even 11. The service wasn't all that expansive simply because it had just started and was using some of Cingular's towers. I have always traveled a lot, so I needed a provider with expansive coverage.
Then came T-Mobile. Being still only 13, it was prepaid. The coverage was wide but weak in my experience. Inconsistent but I found I got acceptible service in metro areas. I switched after about 2 months to....
Sprint. I was at Radio Shack one day and, seeing the new (as the time) Sanyo SCP-8100 camera phone for Sprint service, which was raved about to me at Radio Shack, my parents started me a Sprint account. It was ok at first because I had areas with strong service, but then I also had a lot of dead spots and areas with absolutely no service. I kept the service because of my traveling until about a year into my contract. I bought out of the contract and switched to US Cellular...
US Cellular was EXCELLENT for my area (I live about 40 minutes outside of Frederick, MD). However, as soon as I travel, it switched over to roaming and made traveling a PAIN, an expensive pain at that. I will say, in their defense, that customer satisfaction is always their intention, providing loaner phones when yours is broken... I haven't heard of another company to do that. I ended up researching a bit, looking for an expansive, stable, and friendly service... perhaps with international coverage for when I go to Italy...
Cingular yeilded the most positive results. Starting an account took all of 15 minutes, which is how long it took until I walked away with the black Moto RAZR. Awesome coverage thus far and not a single dead spot yet. I'm very happy with my choice and can't wait to try this service out in Europe!

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic