Verizon was the “undisputed leader” for overall network coverage and reliability, RootMetrics found. The New York-based carrier ranked first in all six categories tracked in the survey, which also include speed, data, voice calling, and texting. AT&T ranked second nationwide in every category except voice calling, where Sprint grabbed the second place.

The rankings, which were calculated by testers in the second half of 2016, are the subject of constant bickering among carriers. Regardless of the test results, consumers have been increasingly switching to the two smaller carriers, Sprint and T-Mobile, as they have improved networks and were first to offer low-cost unlimited data plans last year.

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Verizon immediately touted the latest results as proving that it still had a better network than competitors, in effect justifying the higher cost of its service. T-Mobile rejected the results and pointed to other kinds of tests, such as those collected by Speedtest.net from ordinary customers, where it ranks better. Sprint pointed to its improvement in the RootMetrics results versus earlier surveys. AT&T (T) stayed out of the debate, declining to comment on the latest results.

“We’re extending our lead, it is not diminishing,” Nicki Palmer, chief network officer at Verizon, told Fortune. “That is true on the city level and it’s true on the state level. We’re unbeaten in 48 out of 50 states.”

Verizon won all six nationwide categories for the second report in a row, the survey firm noted. “Verizon delivered excellent performances across all levels of our testing,” RootMetrics concluded.

The Verizon win was anticipated, as RootMetrics posted the results of each city survey as it was collected during the second half of last year. Verizon (VZ) added new technology to its 4G LTE network last year that allows mobile phones to connect to its cell sites via multiple spectrum bands at the same time, a technique known as carrier aggregation, thereby helping improve its results, RootMetrics said.

T-Mobile (TMUS) said that network results reported by actual customers were a better measure than RootMetrics’ professionally surveyed results. Speedtest.net reported in August, for instance, that T-Mobile customers’ average reported download speed matched that of Verizon customers, while its average upload speed was faster.

“In a 2G world, these studies were everything,” Neville Ray, T-Mobile’s chief technology officer, wrote in a blog post. “You needed paid consultants to drive around and measure network performance. Today, everyone is walking around with a frickin’ supercomputer in their pocket, and those smartphones can now tell us almost everything about network performance—with more granularity, better personalization and billions more data samples.”

RootMetrics said its testers drove almost 250,000 miles and collected 3.7 million sample results, both while driving and at 4,200 indoor locations. It posted the results from all the tests online.

Sprint (S) set a record in the latest RootMetrics report with its best-ever performance across the individual 125 city rankings, John Saw, the carrier’s chief technology officer wrote. Saw also emphasized, as does Sprint’s current ad campaign, that the networks of the four carriers are so similar now that customers should no longer differentiate on that basis.

“As I’ve said in the past, we love to win awards, but one carrier ‘winning’ doesn’t mean another carrier is losing,” Saw wrote. “What the other carriers don’t want customers to know, is that all networks now offer a great experience with a difference in performance that is small.”