Is sound genjutsu more powerful than eye genjutsu?
It's not that sound genjutsu is superior. Sound genjutsu operates on a different sense, so that renders doujutsu (eye techniques) useless to escape from it, unlike with illusions that work on vision.

That makes sound based genjutsu more effective on Sharingan users, because they rely on their improved vision powers to counter most genjutsu.