Want to really check which Mobile Network is the fastest where you are? The FCC's made available a free mobile app that tests upload and download speeds. In my office, on AT&T's 3G net, I get 1.04 Mbs download and 1.07 Mbs upload. Check your app store for the "FCC Mobile Broadband Test" if you want to give it a spin.
To check on wired broadband speeds, try some of the sites listed to the right under Net Resources.
Source: "14 Cool Mobile Apps From Uncle Sam," Information Week Government