I have had the following three Carriers and here is how I would rate them:
Verizon Wireless - 1 out of 10: Terrible Customer Service and Expensive.
Length of time with them: Total of about 9 Years
I always dreaded going into the Verizon store anytime I had a problem and was happy the day I paid off my final bill with them.
Positive: Their cellular network from all of my experiences is the best.
AT&T - 4 out of 10: Poor experience with Customer Serivce (on multiple occasions), I had many dropped calls, also very Expensive.
Length of time with them: A little over a year
Positive: They have an excellent selection of phones.
T-Mobile - 8 out of 10: In my opinion T-Mobile is the best out of all three. Excellent customer service and less expensive, and with the direction that they are currently taking in making drastic changes that needed to be made to the industry I feel that they are the best. A negative would be their network, still not as good as AT&T and Verizon.
Length of time with them: Total of about 4 Years
I can honestly say that so far over my lifetime and various other bad customer service experiences; Verizon takes the cake for the worst customer service. I do not care how good their cell service is I will never go back.