It's either Itachi or Obito? But I'm going to go with Obito because he managed to control a perfect Jinchuuriki which Nobody has done before and he controlled Multiple tailed Beasts at once.
the bijuu paths of pain were not because of genjutsu it was because of kabuto bringing the jins back with edo tensei and obito using the gedo and black rods with chains to control them again that had nothing to do with genjutsu, he did however control yagura with genjutsu but it was never confirmed that he was a perfect jin is was said...
itachi is clearly the best in genjutsu he had ka and tsukoyami and izanagi and his finger genjutsu and crow genjutsu and he is the only genjutsu user that can mold chakra for genjutsu while being undetectable to sensor shinobi....obito has one feat itachi has many, and sasuke put a true perfect jin under genjutsu when he put killer bee under genjutsu even though the gyuki freed killer bee sasuke still did it and that was for a couple of seconds before the gyuki broke him free in those couple seconds in tsukoyami itachi would have made those 2 seconds feel like 2 days and would have caused as much damage to killer bee as he did to kakashi...
