For a very long time, the answer to the question in the headline was a simple one. Verizon (VZ -0.85%) was the clear leader in network quality with AT&T (T -0.92%) falling not-far behind.

In recent years, however, the picture has become murkier. One well-regarded study, the RootMetrics Mobile Performance in the U.S. report calls Verizon "the undisputed leader in terms of coverage and network reliability." It also notes that the company's "network reliability results were the strongest among all carriers at the metro, state, and national levels in the second half of 2016."

That sounds pretty clear, but RootMetrics is not the only game in town. A second well-regarded study from OpenSignal showed T-Mobile (TMUS -0.02%) as having the best network last year and the new version of that study shows an overwhelming win for the Un-Carrier.

A woman points to a network coverage map in a T-Mobile store.

T-Mobile has a legitimate claim to being considered the top network. Image source: T-Mobile.

Differing views

RootMetrics and OpenSignal use different methodologies to gather their results. Both believe they have the superior testing method.

Drive testing, which RootMetrics uses, involves testers driving all around the country taking snapshots of network performance. OpenSignal tests mobile networks using millions of real world users testing networks 24/7 under normal conditions, according to a statement emailed to Motley Fool by its CEO Brendan Gill last year. 

Verizon and T-Mobile executives, as you might imagine, profess more faith in the test that has their company on top.

A chart shows that T-Mobile won all but one category.

T-Mobile dominated the OpenSignal report. Image source: Getty Images.

What does OpenSignal's new report say?

In last year's report, OpenSignal noted that Verizon and AT&T scores were hurt by added traffic caused by both companies adding unlimited data plans. The new study shows that both operators recently began reversing their declines. Verizon, the report found, has recovered to pre-unlimited speed levels, but that was not enough to give it the top spot.

"T-Mobile has clearly taken advantage of Verizon's recent misfortunes, boosting its lead over all other operators in our LTE download metric," according to OpenSignal. "T-Mobile is now the operator to beat in nearly every one of our mobile data measurements."

In fact, the only loss for T-Mobile came in "LTE network responsiveness," where it lost to AT&T, not Verizon. To determine the winners, OpenSignal analyzed 5.9 billion measurements collected from 237,213 mobile devices between Oct. 1 and Dec. 30 of 2017.

What does this mean?

T-Mobile will tell you that this report means it has the best network. Verizon will argue that it doesn't because RootMetrics used better methodology.

The actual truth is more shaded. Both T-Mobile and Verizon have top-tier networks. Whether either one is the best depends more on your needs than anything else. "Best" is a very relative term and on a market-by-market basis, the answer varied.

"T-Mobile either won outright or tied for our 4G speed award in 24 of the 33 markets in our analysis, while Verizon won or tied for the award in 23 markets," according to OpenSignal.

That means that where you live and where you travel play a major factor in how you will perceive each wireless carrier. What's fair to say is that the days of Verizon being the clear-cut winner are over. T-Mobile can make its own reasonable "best network" as can its rival.

For consumers, the reality is that either company is probably good enough, but finding the best would require your own testing. Since the majority aren't going to do that, consider both T-Mobile and Verizon viable options for most people.