I did find an article from PC World, however, that shed major light on the issues. I highly recommend it: "A Day in the Life of 3G". The summary:
"During March and April, we spent a day testing the major 3G services in 13 cities across the United States. Verizon's service showed a combination of speed and reliability, Sprint's results lent credence to its 'most dependable' claim, and AT&T's network showed fast upload speeds in most cities."But, read the entire article, and you will learn a lot. The meaninglessness of "bars", for example, and the importance of "backhaul".
And remember: the Network is as important, if not more important, than the Device. And all data service (like politics) is local! Your results may vary, so test them before you commit to a two-year, multi-thousand dollar contract.