I would recommend that you need to get good at multiple characters anyways if you want to be an asset to the team. Dva isn't always useful, and sometimes another pick is better for the team.
I also play Genji, Tracer, Roadhog, Hanzo, Reinhardt, Lucio, Mercy, Zenyatta, and Symmetra regularly. Irregularly, I play Pharah, Reaper, Zarya, and Ana, but I'm not that great with them. I also play Widowmaker, Sombra, and Torbjorn regularly in QP when I want to fuck around, but don't see them as serious picks ever.
McCree, Soldier: 76, Bastion, Junkrat, Mei, and Winston are the only ones I very rarely play, and that may change since I'm atleast slightly interested in playing basically all of those except Soldier and Bastion.
D.Va just happens to by my favorite hero out of everybody.
Personally I don't get people who actually exclude themselves to playing only one character. It feels like an inherent self imposed limitation to the game.