It's been a year since we looked closely at wireless service in the United States, and in the interim that service has changed considerably--mostly in positive ways. The industry is in the midst of another major technology transition, this time moving from a 3G world to a 4G one while trying to grasp the implications, realize the opportunities, and deal with the growing pains. All of this should be good (even fun!) for consumers, and it could lead to a lot of cool, superfast, reasonably priced devices.

In this year's study, we took snapshot measurements of wireless service in 13 cities--Atlanta, Boston, Chicago, Dallas, Denver, Las Vegas, Los Angeles, New Orleans, New York, San Francisco, San Jose, Seattle, and Washington, D.C.--across the country to get a real-time view of how the 3G-to-4G transition is progressing, and of which companies are currently delivering on the promised faster speeds.

SLIDESHOW: 3G and 4G Average Speeds, City by City

For details about how we conducted our testing, see "Methodology in a Nutshell."

In general, the major wireless carriers appear to be keeping pace with the explosion in demand for mobile data service. The 3G service that most of us use today is at least as fast as it was a year ago, even though far more subscribers are tapping the networks with increasingly data-hungry devices. And a new generation of much faster 4G wireless service is quickly becoming commonplace in the country's more populous areas.

"Our research shows that the demand on mobile broadband networks is nearly doubling every year, so there is definitely no room to remain idle" said Dan Hays, U.S. advisory wireless leader for PricewaterhouseCoopers (PwC). "The results of this year's PCWorld study clearly show that most wireless network operators are continuing to invest significantly in their 3G networks, adding capacity to ensure that speeds remain competitive."

Here are the major findings of our study:

• AT&T's new LTE network turned in the fastest download speeds of any 4G service. Its 3G service was very competitive, too--and those two results help make a strong case for AT&T dual-mode 3G/4G phones.

• T-Mobile's HSPA+ 21 service won in the 3G bracket of our study, and the company's high-end HSPA+ 42 service competed reasonably well with other providers' 4G service. In addition, T-Mobile's service plans are more flexible and its prices are lower than those offered by competing carriers.

• Verizon makes 4G service available in many more locations than other providers do, and its 4G upload speeds are top-of-the-line, but its 4G download speeds don't match AT&T's. And Verizon's 3G speeds are not improving much, especially when compared to the competition.

• Sprint was consistently a laggard in our wireless speed derby. The company seems to have virtually stopped developing its existing 3G and 4G networks while looking for a way to make the transition from its outdated WiMax 4G technology to LTE.

Next page: How AT&T performed.