@mawr I don't think I actually see a practical difference between Friday and Monday, 'cause whatever day of the two we pick will become part of "the weekend" and the functional "work week" will start on the first day back to work.
That said, I'm more inclined to argue for "Monday" as the day off if only because it has such a terrible rep and I would rather rehabilitate it by making it the "productivity day not at work" (plan the week, pay bills, recover from the hangover, et cetera).