My favorite long-time cell phone company has been Qwest. Everytime I go out and comparison shop, I still keep coming back to them. They even gave me two weeks free so I could review other companies and still keep their service. When money was tight they worked out a plan for me so I could still afford a cell phone.
What I love most about them is they work with me and the customer service is always helpful and supportive. I never have to wait forever on hold or be the bad guy in order to get my problems solved. While their coverage area is not as extensive as the competition, they have been a great company for me.