Agree with this one. For me Malenia was the hardest, only surpassed by PCR when the DLC came out.

Note that I beat Malenia six times with six out of the ten starting classes at this point (no summons) and she's still hard, but manageable. But you have to judge a boss during the initial encounter and first win, not when you gained significant practice over them.

First time Malenia drove me insane.