I have used Sprint, AT&T wirelss, GTE, and Voicestream.
I like Voicestream a lot because:
1) Service area is better than Sprint in Dallas/Ft Worth. There are so many dead spots using Sprint, it is not funny. AT&T coverage has been ok.
2) Customer service has been great. I cannot remember how many times I wanted to bang my head on the wall with Sprint. At&T had fine customer service, no complaint there, but Voicestream has been the best.
3)I got 2 free phones, with wireless kits and car chargers, for free. And I have a 4000 minute plan for 70 bucks a month. This is great for me and my wife's long distance. I did sign a 1-year contract with VS, whereas with Sprint I did not have too. But the contract does not bother me because of the plan I have is more than sufficient. And with Sprint I was CONSTANTLY being charged for roaming, even when I never left the calling area or even my freaking city!!!
4) Their 5 state coverage is better than the 4 state I had with Sprint and AT&T last year. I have not tried their national offerings.
I worried at first because VS is new in my area, but so far I have not a single complaint. Been using them about 3 months.