I've tried them all. It comes down to coverage and cost. It's awfully gratifying to hear the flight attendant telling you it's ok to turn on your mobile phone at your international destination only for you to happily comply. Searching ... searching ... and ... Bing! I get a text that welcomes you to the country you've just arrived in - all before you reach the gate! And, the best part is you can begin communicating via text and cellular data straight away. Awww ... all is right with the world again!
Disclaimer: I am not affiliated with nor receive any compensation for this public service.
Notice that voice calls will cost you, but who calls anymore? Mobile data rates are around the 2G speed, but hey ... beggars can't choosers, right? For T-Mobile, some of their plans offer this service as part of your mobile plan. Here in the States, their service is pretty good, but not great - especially in more remote areas like the wilderness.
I know that other US carriers allow you to buy a months worth of international access - I would highly suggest you check with your carrier before leaving home; in this connected world we live in today, it's often comforting to know that you can stay in touch with those who matter.
Sending out instagrams or fb posts in realtime is just plain fun these days, isn't it?
If you're looking for more validation from other sources, check this article out, https://www.cntraveler.com/story/t-mobile-simple-global-the-best-cell-phone-plan-for-travelers-just-got-even-better