Wow. How off a review can be. T-Mobile's coverage is generally solid in urban areas, but drops off outside those urban areas. I review phones and service in the midwest and even in Chicago and the Chicago suburbs T-Mobile's coverage is spotty. Strong, then drops off, strong, then drops off. Or in the case of my neighborhood well outside of Cook County, IL, no signal at all. Decent customer service and "all you can eat data" doesn't really do you any good if the service doesn't work where you work and live. If you don't travel much, and T-Mobile works where you live and work, great. But if you travel quite a bit, I'd think twice about going with T-Mobile.
In T-Mobile's defense it has supported Wi-Fi calling for sometime, and has even expanded it to non-phone devices from Apple. More on that here: https://support.apple.com/en-us/HT203032.
As far as your review of Cricket goes: I suggest you try again. Cricket now uses AT&T's network, so coverage is great. Solid voice and data coverage, at least in the midwest. Uninterrupted voice and uninterrupted 4G LTE coverage from Lake Michigan in Chicago west to the Illinois-Iowa border. You can't say that for T-Mobile. No, Cricket's LTE speeds can't match T-Mobile's speeds. This is likely to due to two reasons: Cricket throttles upload and download speeds and it piggy backs on the AT&T network which historically has seen much more data usage due to its long-time alliance with Apple and iPhone users who hog up most of the 4G data bandwidth in the US.
I'm not basing my opinions on single phone or service either. I have and support many cell phone devices. I currently pay for service to: US Cellular, AT&T, Verizon and Cricket. I have also had service through Sprint and StraightTalk. I have family with the iPhone 6 through T-Mobile. I have recently reviewed or used: iPhone 6, iPhone 5s, iPhone 5c, Google/Motorola Nexus 6, LG Flex 2, Samsung S6 Edge, and a Moto G 4G LTE (2014), in addition to two LG and Samsung flip phones and a wireless phone base station.
If you are an average user reading these reviews: ignore the reviews. Test the carriers yourself. Don't be afraid to return your phone in the week or two you are allowed to test it. If your new phone and service doesn't work, return the phone and cancel the service and try another service.