I vote Winston. I think he can be a better hero with slight adjustments. Maybe give him 1000 health. Or add an ability. During ultimate beast form, press RB to drop a bunch of bananas, cooldown 2 seconds. You can drop a total of three bunches during ultimate form. Any player, including the enemy team, gains 50 health.
Doom needs a rework the most out of any character. Doom has over 70 bugs in his kit and a lot of them can be reproduced. Every new update breaks his kit even more to the point where it’s better to start over than to fix the bugs.