Dark-horse mobile carrier T-Mobile for the first time rose to the top spot for cellphone service performance in Denver, according to a national survey set for release Tuesday.

Independent monitor RootMetrics’ biannual survey found the nation’s largest carrier, Verizon, maintained the top spot for overall performance in Colorado during the first half of 2014.

But Verizon, which has laid claim to the title in Denver since the survey began in 2011, was caught by T-Mobile in a tie for the crown in the metro area.

“We are seeing T-Mobile making huge gains in the major metropolitan areas, and Denver happened to be one of them,” RootMetrics CEO Bill Moore said. “This is one of the few markets in the country where T-Mobile tied or outright won every category in a market.”

Of the remaining five categories, T-Mobile won in speed, text and data performance and tied for top dog in reliability and call performance.

Last year, T-Mobile was tied for second place in overall performance and third place in reliability in Denver, “so moving into first place in all categories is substantive,” Moore said, “We usually don’t see that.”

Andrew MacFarlane, CEO and founder of Denver-based Mobile Pulse, which collects performance data for companies, said its assessment also shows a T-Mobile surge in Denver.

“From a performance perspective, downloads and such, T-Mobile is definitely the best,” he said, but cautioned, “T-Mobile is actually the least reliable in terms of call failure and connection speed.”

Mobile Pulse ran 230,000 tests in the city and county of Denver between Jan. 1 and Aug. 18.

In late 2013, T-Mobile tied or won the No. 1 spot in only two on the 125 U.S. metropolitan sample areas RootMetrics tests. By the first half of 2014, the carrier surged to the top in 25 of those cities.

“What changes is that as you get out of the major metropolitan areas, T-Mobile is less strong in the rural areas,” Moore said.

For overall performance across Colorado, Verizon is the clear winner, as well as in speed and data performance. Verizon ties AT&T in reliability and call performance while AT&T is a consumer’s best bet for texting.

There are two tiers of mobile carriers, Moore said. Verizon and AT&T have long had an advantage over T-Mobile and Sprint in their coverage.

“Verizon and AT&T are a clear step ahead on the national and state basis, but at the metropolitan level it is a significant horse race,” Moore said. “All four are getting faster and becoming more reliable.”

Sprint ranked last among the four major carriers in every category in Denver and Colorado.

“Sprint is in bad shape because they have not launched 4G. Period,” MacFarlane said.

RootMetrics’ leadership sees Sprint as the darkhorse nationwide, Moore said, “because they are poised to make some significant gains if they pull off their new technology deployments.”

RootMetrics uses consumer-based behavior for its methodology. Using Android devices purchased directly from each carrier’s stores, its team of a couple dozen researchers drove more than 234,000 miles across 50 states, gathering more than 5.6 million samples.

In Denver, RootMetrics employees drove 1,200 miles taking 26,000 tests in the first half of the year, sampling both indoor and outdoor spots.

“You and your coworker sitting next to you are going to have different network experiences because you live and work in different neighborhoods,” Moore said, which is why he encourages consumers to use RootMetrics’ neighborhood coverage map to compare carriers, block-by-block.

Kristen Leigh Painter: 303-954-1638, kpainter@denverpost.com