I got off easy with doing Set Theory with Greggo. I know that Cummings once taught it ... and assigned 6 homeworks! That class must have been impossible.
EDIT: I just read over their final ... and it looks as hard as either of the math studies algebra finals.
You can count math studies as up to 5 classes, since that's the number of normal-track classes it covers.
Also, having TA'ed graph theory for pikhurko and mackey, and having TA'ed 251 twice, I still see 251 as the hardest.
Of course, I might also say that I five-sixths assed Math Studies and three-halves-assed 251.
Maybe I shouldn't have rushed to make that statement. It certainly made graph theory with Mackey look like kindergarten, but I'm now remembering the stories about graph theory with Pikhurko and Set Theory.
P.S.: Hacker News is a proven way to break reddit addictions. Welcome!