So far the 2 most fun to use champs I've played.

Teemo and Twisted Fate. I was just on a role with TF. just bought him and I won and like 7 out of 9 games. and did well on all of them except one because of a diamond 4 that raped the entire team

I have Diana, victor, Rengar. Riven. and few others and the two above are the most fun to use. i dont think ip cost has to do with how fun a champ is to play.