I've used both. Love the 85L II.
Get the 85L II if you want best IQ, best looking bokeh, and razor sharp images at f/1.2. It is also more reliable than the 50L in terms of focus accuracy, and it doesn't suffer from the pesky focus shift issue.
That said, the 50L is still a nice lens. Just not as good as the 85.
But I should warn you that that the 85L II has a very slow AF. I can live with that, but can you?
See, this doesn't make sense if you are buying a lens for general use and usable focal length. If people buy lenses based just on IQ, why not just buy the 200 2.0L, since it's the sharpest and most bokehlicious? It's like saying: I really need a pickup truck for all around purpose use, but a everyone says the Corvette is sooooo awesome, so I'm going to get that instead.
Of course, there are always caveats, like if the only thing one is after is sharpness or bokeh. In that case, disregard the above.