I have a 50mm f1.2L, and i have a non L 85mm.
The 50mm is my absolute favourite lens on my cameras, (i have a 5d2, 7d, 550d). If i never had to take a lens off it would be that. I usually have it on the FF and have not had the focus issue that an earlier poster mentioned.
My non L 85mm is also a beautiful lens, obviously the L is the grandaddy of primes so the quality/focus/iq is different to my S___ty non L, but obviously focal length is the same and unfortunately i PERSONALLY don't find as much use at that focal length, if i really did need that focal length I'd switch bodies, although that isn't an option in your case.
I recommend hiring both, and hiring a 5d2 body (or borrowing someones) as they are both exceptional lenses and at the end of the day it comes down to how you are using it, and what works for YOU. They are a pricey bit of hardware and a couple of hundred for hiring is nothing compared to buying the wrong one!
This is just from my personal/professional usage, i'm not an expert that most people on here are!