2 races I think are just ridiculous:
Gulliver: simply for the fact it spawns with HP, leeches HP, and has an ultimate that gives it HP, so you end up with around 250HP to begin with, you can keep getting HP with the ultimate (can't remember the cooldown) and you can buy HP so you can end up with over 400 HP which is stupid in my opinion
Another race which left my head while I was typing: Yeah, it's so OP. It's all "I was a race in your head, then I left" and I was like "get back in there" and it just ruins the game for everyone really when you lose a race from your head!
Anyway, that's my input