There are many many threads on this same topic. The best answer is always the same. Get a pre-paid sim and test it out in the areas you frequent. It's great for some, not for others. Better in big cities. WiFi calling works wonderfully. You can get a "free" WiFi or LTE CellSpot for your home. If you travel internationally, it saves a lot. T-Mobile has improved significantly in the past 3-5 years. Anyone who had it more than 2 years ago and says coverage is bad lives in a different coverage time. My service on TMO is better than it was on AT&T when I left 3 years ago and continues to improve.
They also have T-Mobile Tuesdays where you can get discounts and free things. I get weekly Lyft discounts, free magazine subscriptions, Fandango movie rentals, and I believe they are giving away MLBTV to customers again this year. They've been doing it for a couple of years. They were the first to have free 4g/LTE roaming in Canada & Mexico. Free international roaming speeds are 2G/3G but works well enough in all the places I've traveled (All over UK, Ireland, Netherlands, Belgium, France, Spain, Norway, Philippines, Czech Republic). WiFi is everywhere in all of these places also so WiFi calling is awesome and you're never in 2G/3G land for too long. You can always get a call or text. Good enough for Social Media or pulling up maps. Last summer they had free 4G/LTE international roaming for the month of July, which was perfect timing on a 3 week trip I was on.
But if service doesn't work for you in the places you need, none of the above matters. So testing it is the best advice.