I owned the 50L and it was one of my favorite lenses for a very long time. It had it's quirks on the 5D2, but when you nailed it you really nailed it. On the 5D3 it was 10x better. But I shoot video mainly so I eventually got rid of it in favor of the Zeiss 50mm f/2 Makro. It's way sharper on the edges, definitely sharper in the center. But at the same time, I still miss my 50L and will probably get another one.
As for the 24-70 II, I've spent maybe a week total with it, and it's an amazing zoom, definitely one of the best in Canon's lineup. Definitely sharpest on the wide end, and that would be a good thing since the 16-35mm is kinda weak at 24mm. It's overall an excellent lens.
But it's your call really. Do you find yourself wishing you had a good walkaround zoom? Then get the 24-70mm. But it seems to me that you have taken a liking to the 50L, and if you have maybe you should go with that. As great as the 24-70mm is I've always found 24-70mm zooms to be a bit dull. Yeah they are very practical/convenient, but they just aren't very special, you know what I mean? It's just not a lens you get excited about strapping on your camera. Now a 50mm that opens up to f/1.2, that gets me excited.