+1 Sounds like advice from an owner.
I do a lot of event work with a 5D3/70-200L 2.8II and a second 5D3/50L. I love the 35L but once I shifted to the 5D3s, the 50L is just about the best lens for me. It's my standard carry when I go for one rig. Great portrait focal length, pure cream bokeh and now, with the AF of the newer bodies... it's killer combo. For event work it shines, and gives the unique 50 perspective... great for photojournalism. The 50mm 1.4 is ok, had the same experience Random Orbits... cheap build and if your making money can take a crap on you when you need it. It also hunts in sketchy light. Not the 50L though, locks on and its built like a tank. Love my 35L too but it now takes a back seat and with the new Sigma, I'd be checking it out too. I own 3 Siggys and the all perform flawlessly and are built well, so the 35 is looking like something I might need to try.
I'll probably keep the 35L until after the 35L II is out for a while and the prices soften. I mostly use it for portraiture and as a walk around lens, so I don't need it to be critically sharp into the corners because my subjects aren't in those locations anyway. Most people know that the 24-70 II is sharper than the 35L, but according to TDP, it is also sharper than the Sigma 35, so in either case, the user that is concerned about sharpness the most will opt for the 24-70 II in either case. Canon's next generation primes should be able to beat the 24-70 II. If not, then Canon will lose potential sales because more people will opt for the 24-70 II rather than buying a few primes with higher total sales within that focal length range.
I own the 24-70II also... in reality and real world use the 35L and the 24-70LII are very similar. I still prefer to carry the 50L over the 24-70II due to it's low light flexibility. Especially in the event photography arena, sometimes a flash can't be used and dropping below 2.8 is a life saver.