I would say Ahri or Diana for mid domination. Ahri can get out of ganks easily and loves to roam, plus if you get good with her passive plus orb, you can stay in lane for quite a while.
Diana, well just because she is tough early game, and can setup some create initiations. She is a safe mid pick most of the time. Although, I have seen her banned frequently as well. Last night alone out of 4 ranked matches (1300ish) she was banned every single one of them. I think people saw how powerful she was at IPL5 and just got scared of her.