for portrait I have a 70-200L 2.8 II and a Macro 100L 2.8 IS, I use the lens on a 5D mkIII.
I have tried the 50L on the 5D III and it is fast and super sharp, I have read a lot of negative comments about this lens but my experience was very positive. I had a very short time with a 24-70 II at B&H today and it was a lovely lens.
The newer-production 50L is a great lens on 5D III. It really is. I shoot people with it never going narrower than f/2.0, where there is no peer in the 50 mm lens world.
But if you don't already have the 85L II, especially on 5D III, I would save my pennies and get that first. Just shot an event with 5D III + 85L II combo, and holy Wowza I only hope SOMEBODY comes up with (auto-focusing) 50 mm with 85L II's picture quality.