I own both the 35mm f/1.4 as well as the 50mm f/1.2, and what it really comes down to is testing both lenses out. When I had to first pick between the two, I rented both and considered which focal length I would get more use out of, paired with my current lens line-up at the time, until i could afford both. You've picked two of Canons best primes (in my opinion) and they've never let me down.
On a side note:
With all of the talk about an up and coming 35mm f/1.4 ll, has there been any hint as to an update on the 50mm f/1.2? Some people are saying that the 50's are fading away and becoming a thing of the past, while others say this L is due for an update (although, how much more can they update this lens?) comes to mind.