If you could have 20 kills on a champion, who would it be and why?

1: As the title suggests: which champion would probably carry the game the hardest in your opinion if they were fed 20 plus kills?

Also

2: Which champion would be the least useful with 20 plus kills?

From personal experience, the champion I felt I could carry the easiest with when fed was Kassadin. The game felt like I was playing on cheat mode.

I felt useless late game as a fed Qiyana (yes, I’m bad I know that) perhaps because I didn’t use that lead and I felt that the enemy tanks took no damage.