50 or 85, somewhat confused here ...

Hi Guys!

I'm looking for a REALLY GOOD prime. So if you had to choose ONE of the following lenses to add to your arsenal, which one would it be and why (keeping in mind the FF body).

Both are primes:

Canon 35mm f/1.4L
or
Canon 85mm f/1.2L

I currently have the following

Canon 50 f/1.4 (not happy with the focus/lock performance of this lens)
Canon 17-40 f/4L (very slow when it comes to low ambient light situations)
Canon 70-200 f/2.8L

Any info will be most appreciated.
--
Regards,
Dave