The problem with these studies is that they all omit what is probably the most crucial factor of wireless service - COVERAGE. T-Mobile might be faster than AT&T, but they have a long way to go to match AT&T's coverage footprint.
That's my issue. I'd switch back to T-Mobile in a nanosecond if I could, but their coverage both at my work location and where I live is horrendous. I frequently had dropped calls, data connections would drop from LTE down to 4G and texts would sometimes take 10 minutes to send/receive. I've had no such issues with AT&T at all, so I'm forced to stay with them and pay more...for now.