No, I haven't tried steam VoIP because as mentioned, the game engine itself usually comes with a working and tested solution, so why bother using any other VoIP application that's just wasting RAM and CPU cycles trying to do the same thing in a far larger footprint?
In the case of Overwatch you can group up with friends outside the game and share your own voice channel with each other, but when you join a competitive match you have to choose between group chat and team chat, and most people expect you to join team chat.
In other words, if you and one friend join a game you can either talk/listen to that one friend alone or the entire 6 man team, and switching between the two requires multiple menu clicks.
So we use Teamspeak alongside the game to allow us to talk privately with each other seprate from the whole team in game. With any modern gaming PC the "wasted RAM and CPU cycles" are negligible.
