AT&T and T-Mobile won some praise from PCWorld after the publication released the results of a nationwide test to find the fastest cellular networks.

AT&T’s 4G LTE network clocked the fastest averages, though Verizon’s LTE network edged out its rival for upload speeds. T-Mobile was the clear winner in the 3G race, for both uploading and downloading.

Sprint’s network speeds came in dead last in all testing cities, and its 4G WiMax offering was behind even 3G network speeds from its competitors. The company is looking to convert its WiMax network to LTE, and, according to the report, has focused the bulk of its development resources on that conversion.

The testing ran in 13 cities around the country: Atlanta, Boston, Chicago, Dallas, Denver, Las Vegas, Los Angeles, New Orleans, New York, San Francisco, San Jose, Seattle, and Washington, D.C. AT&T’s 4G network was only measured in 11 cities, as the carrier doesn’t have the high-speed coverage in Denver and Seattle. New Orleans was excluded from Sprint’s 4G results for the same reason.

The report showed that coverage in the Washington area reflects the nationwide results, though T-Mobile’s 4G network fared a bit better when it came to download speeds. The D.C. results also indicate that AT&T’s 3G network in the area isn’t as strong as it is in other parts of the country. In fact, the District had the worst results nationwide when it came to AT&T’s 3G speeds.

Overall, however, the results showed that carriers are continuing to build out their 3G networks and adding capacity to keep up with mobile growth.

Growth rates are significant. In March, Nielsen reported that smartphones now account for half — well, 49.7 percent — of all mobile phones and that more than two-thirds of all those buying a new phone opt for a smartphone rather than a feature phone. That means a lot more demand for data at the same (or faster) speeds that consumers have come to expect.

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