Samsung Galaxy S III (S3) looks identical across all four major U.S. carriers, data speeds are anything but equal. I've been testing GS3 phones on one carrier or another for over a month now, and was curious which one gave me the fastest and most consistent speeds -- and if the two were the same.
"Fast" is, of course, a relative term. So many factors affect data speeds, from how well each carrier can cover your neighborhood, to architecture that could block your signal, to a high number of users that could congest the network at any given time. Fluctuation is therefore normal, and the absolute "fastest" speeds harder to pin down.
There's also the question of diagnostic speeds versus real-word tests. Throughout my testing in various San Francisco locations, I used the Speedtest.net app to measure the download and upload speeds for each phone. I also used real-world tests to visit Web sites and download a common game.
My time tests certainly won't match up with any you conduct in your own cities and neighborhoods, and I'm not suggesting that the outcome of my test is true every time in San Francisco. Carriers continuously build out and upgrade their networks across an urban or rural market, which means that the data speed landscape is very much in flux.