Which phone company is better, metro or sprint? & why.?

So far I am liking Sprint a lot better as a sometimes user with Project Fi than I ever did as a Sprint customer.
It really depends on who has the signal where you need it.
I think Metro has improved since the T-Mobile merger, I have seen people using it without going outside recently.

This CNet article might be useful
https://www.cnet.com/news/comparing-wireless-carrier-plans-us/

YOUNG METRO