Verizon is by far the best in terms of coverage in central and western USA, AT&T is second. Sprint/Nextel are worthless if you get more than 5 miles of an interstate. If you want a cheaper plan look at Walmart Strait talk (prepaid plan) they can use either (but not both) Verizon or AT&T towers for quite a bit less money.
Update: We didn't go with Sprint...ended up at Cricket (not prepaid) They have a similar deal to the one Sprint had, but way better coverage (they use AT&T's towers) we could hardly find anyone that liked Sprint, but the ones we found that had AT&T/Cricket were happy and would still switch if they had it to do again. This will cut our cell phone/internet data plan cost to almost half for us...
I use a prepaid service from US Mobile, they use T-Mobiles line. Good service and cheap (the way I prefer) I see you went with cricket but if get tired of them, check out US Mobile, I don't get anything by recommending them so no catch. Personally I wouldn't use sprint or any carrier that uses their network, I've met a few people who use them and nothing but complaints about service in their house. My one friend use to have to keep his phone by a window and sometimes stick his head out the window to use them. This was about 6 years ago so maybe they have become better?
Been with Sprint forever! It is the only provider for me that I can get service at work in the buildings. Verizon users have to go outside in the diveway and stand on one leg with the phone up in the air and AT&T users have to drive down the road a few miles. Gary