In terms of versatility and skill without a doujutsu Kurenai probably has the best genjutsu that we've seen, the sharingan is just too good at seeing through them. Next to Kurenai is Ma and Pa via frog song.
But when including the sharingan, then Itachi or Shisui probably have the best genjutsu, though we haven't had a chance to see what Madara is capable of with genjutsu. I can only assume he has Tsukyomi since his plan involves placing the entire world under a more intense/powerful version of it.
Overall I have to give it to Itachi, his skill with genjutsu has been shown to surpass anyone else we've seen, Izanami, tsukyomi, and even his regular genjutsu are all powerful.