Gah. ロマンジはよくないよ。
Another way to phrase this would be:
なん アニメーが いちばん すき ですか?
It has been a while but I think you just asked what anime do you like instead of favorite. Please correct me if I'm wrong as it's been 2 years since I last studied Japanese.
As for my answer: Anime is a bit tougher...