I had to include a support hero, so Lucio is the obvious choice. But the main key to playing him is that you need to move. A lot. Move around everywhere on the map, but keep your allies healed up. A good Lucio knows when his team needs heals or when his team needs speed. In some cases, it's pretty obvious. You speed up when you want to quickly secure a point and then pop the heal.
But the truly great Lucios mix and match speed and health to give their team the upper edge. If any enemies get too close, you can right click and you will literally blow them away.
I wanted to go with Mercy as an easy hero, but her lack of damage (that tiny pistol, really?) would probably turn some people off.
What are your favorite Overwatch heroes to play? Let me know in the comments!