Doomsday the easiest Champ? I must disagree, because Gas Cat says that she would like a word with you.
And as RealName points out, K/D/A ultimately means nothing. My best game to date was a 40-4 as Flash (post knock-up nerf) and I ended up losing the match. So apparently one competent player with four new players loses to five competent players who work well as a team.
And the tier list is a great step in the right direction, BUT it can be misleading. For example, Flash is one of my mains. I have stuck with him through all of the nerfs. I feel as though if he can just get a higher scaling on his Q, then he will be in a perfect spot. But on to my point: A competent Flash player will do well, and most likely help the team secure a victory. BUT a bad Flash player can easily cost your team the game.