In my opinion, the best cell phone company is Apple. The company features new phones with a lot of features and ones that have the best quality. They have a good timing in the warranty section and they never go wrong with their warrants.
According to numbers, Samsung would be the best choice. At the end of 2011 the sale growth for Samsung was a 33% increase while Apple saw a 14.6% increase and Nokia 14.1%. I just got a Samsung GT-I900 Galaxy and I must say that it is great. Works on Android and great screen resolution. If you were to buy a new phone, get it from either: Samsung, Apple, Nokia.
If you are talking service provider, I say Verizon. I have had them for 10 yrs now. Had one problem with one bill, and with one phone call it was fixed. I have also traveled many places in this country and always was able to get service except in places where no cell towers were allowed. My husband had Sprint for awhile and calls often were poor quality. 1/2 my family has AT&T and they are the only ones I get "All circuits are busy" with.
I've been to loads of phone companies, and so far Tmobile is the best. They don't have iphones :( but it's not super expensive and the customer service is pretty good. Verizon and Sprint have crappy customer support and don't care if they are overcharging you, and AT&T just overcharges you straight out.