Alot of articles and videos I've watched he'd have said Genji and tracer are your best bet for ranked but personally I really like D'va she has the ability to carry games with little help as long as you know what you are doing.
Pharah. The rewards are evenly distributed as follows:
1. Lower ranks can't aim, so even hitscan will struggle against you.
2. if no hitscan is selected you can (and likely will) kill literally the entire enemy team with relative ease because a direct hit deals 120 damage + splash to other nearby enemies.
Any support. Most wall want to be dps so you will always fight for that till higher up. Zen is a good mix of both and rewarding. Once you climb high then a 2nd account for dps is what a lot of people do. You'll learn a lot by then and hopefully be a much better player understanding how supports work. Low Genji mains, as one example, always blame heals because they don't know how support works. With that knowledge you would already have an advantage over many and know when to engage and when to disengage.