The only thing that matters when you're trying to pick a wireless carrier
More for less. Better. Faster. It's easy to get wrapped up in mobile network carrier marketing.
Apart from the cost of a carrier's plan, only one aspect matters. That's whether you get a decent signal where you live, where you work, and the space in between. The fastest network does squat if it's not available in your area.
Of course, calling and texting matters, but you can mostly get by a lengthy conversation with even one bar of signal strength on the relatively old and slow 3G network.
If you're a heavy data user for streaming music or video during a commute, you might be inclined to research which network has the fastest 4G LTE speeds to ensure the smoothest possible stream. With full signal, however, the 4G LTE that most carriers broadcast is fast enough for most streaming needs. Once you start getting down to one or two bars while commute-binging on a Netflix orginal series, you may start seeing the loading symbol which translates universally to "you-have-rubbish-signal-consider-changing-your-carrier."
If you often disperse out of the home/work zone, you may want to cough up the extra cash for more expensive carriers like AT&T and Verizon for a better chance of maintaining strong 4G LTE signal.
Verizon and AT&T currently have the widest network coverages, with Verizon even claiming that 98% of Americans are covered. But they also tend to offer the least value for the most limited plans. T-Mobile and Sprint offer tempting plans for talk, text, and data with great value and flexibility, but at the cost of limited 4G LTE coverage.
If you're not so tied to technology, you could save yourself a few bucks and go with carriers that offer more value at the cost of 4G LTE coverage. T-Mobile is one of those carriers, and I asked some of my colleagues in New York City who use T-Mobile what they thought about it. They say coverage is great until you step foot outside the metropolitan area where 4G LTE coverage starts to become non-existent, and data speeds begin to crawl. They claim to rarely leave the city, but they seem to survive easily enough when they do.
You can check the carrier's website for coverage maps which give you a general idea of the extent of their 4G LTE coverage, but they're not always fully accurate. There's no better resource than the humans using these networks, so ask around to see which carrier has the best signal where you are, or where you're going to be.