Cool thread!
I main D.Va as well and to a lesser extent Reinhardt, Wrecking Ball, Mauga and Hazard.
For Supports, I have some mild preferences.
I hope to have a Mercy. I have a soft spot for Mercy mains. They are so sweet and adorable (especially the Pink Mercy mains). 
For the other main, I prefer Juno, because shes my Support main. Love that girlie! 
But really any Support is great. All of them do well at healing and having a Main Support of any of the heroes on my team is always a treat! 
My least favorite is a Lifeweaver support. Usually, they do not know when to use Life Grip properly. Even the ones that have good timing cause a disruptive gaming experience. I easily get dizzy from suddenly movements (no spinny rides at the fair!), so being yanked around is very jarring for me. But if they use their Life Grip sparingly, its not so bad. Then theres the Petal Platform. Again, improper Petal Platforms are very annoying. Most Lifeweaver players dont use them right.
Its always nice to see a Baptise on my team. Hes one of the rarest supports I see. I used to main him before Juno came along, so mad respect for the players who play the coolest brotha in OW2 