I have Hangouts on several devices and I have not experienced the echo issues that you are having. The only thing I can think of is there may be an issue with the type of device you are using. Is it...
Yes, Cricket is now AT&T.
If speed is important to you then GoPhone is your choice (and Cricket, to a lesser extent).
I really wish we knew if porting from a prepaid provider counts for the $150 credit.
Trickle-up competition. T-Mobile usually starts with something then it goes all the way up, even to Verizon.