You could say Kaguya, but then again most people do not include the sage and their descendants, because they were the best at everything, especially Kaguya, considering that at one point she held all the power.
-Shisui had one op genjutsu, but he could only use it once a decade. Other than that he's featless.
-Itachi has the best feats with genjutsu and his entire fighting style revolves around it, he's the only Uchiha shown to cast non-ocular genjutsu, he is the only Uchiha stated to have the ability to control people from beyond a sensor's range, and even w/ his 3-tomoe genjutsu you won't realize that you're in it initially. Itachi is the best genjutsu user. U_U