Consumer reports issue for Jan 2009 is out and the ratings for cell phone companies are not surprising.
Overall for customer service(best to worse).
In terms of service availability in the Los Angeles area(best to worse)
Ranked by reader service score.
When ranked by connectivity:
Note: T-Mobile had the worse service availability, which I can attest to personally, I can drive for miles on the 134 and not get service in the Eagle Rock and Glendale area, between the 2 and the 210.
AT&T had the worse static on the line, which I have experienced.
These reports are not surprising based on the everyday complaints we hear.