ComputerWorld has posted a review of the three available 3G networks in the US. They pit AT&T, Verizon, & Sprint against each other in terms of service availability & speed using cellular network cards from each on a Lenovo X300.

"I timed how long it took to establish a connection with each network, followed by speed tests. Using Alken's bandwidth meter, I was able to gauge download and upload speeds as well as how long it took to load that vendor's home page."