Its not about who the best champion is, its how the players skill varies between champions. You need to select a champion that fits your standards and abilities. There is no such thing as a bad champion or a bad player after all. Some champions may be "OP-er" then others but the ones that are not so powerful you may be able to use better, making that champion stronger for YOU. Although i said all this i do have a few suggestions up my sleeve.
- LeBlanc is said to be powerful but can get squishy.
- Nidalee is a fun champion to play.
- Others like Xin Zhao and Gragas make good champions depending on your abilities. If not it can be a complete disaster if you don't practice.
Good Luck Selecting!