At the NECCC conference this past weekend, I was able to test a few 85 mm lenses. This is a great focal length for portraits and for creating lots of creamy bokeh. They also tend to be pretty sharp since they are prime lenses. I tested the Olympus 45 mm f1.8, Rokinon 85 mm f1.4, the Canon f1.2, and the Panasonic Leica Nocticron 42.5 mm f1.2. Sony also has an 85 mm f1.4 G Master wich is supposed to be very good but I didn't test that lens since I don't have a Sony camera.
First of all, I would like to shot two images to show why you might want a lens with such a wide aperture. It's certainly much easier to shoot with an f2.8 or f4 lens but you just don't get the same amount of bokeh. Here is a shot taken with the Rokinon f1.4 and one taken with the Canon 24-105 mm f4.
As you can see in the first image the background is more blurred. The bokeh is also affected by distance and the model on the right may have been a little closer to the wood but in general all of those shots were sharp throughout.
I was shooting both of the above lenses on Canon bodies. The Canon F1.2 is an amazing lens and produces a very unique look. I had heard the autofocus on this lens was slow. I didn't find that to be the case but focusing was a challenge at f1.2 and many of my images were out of focus. I wasn't using my camera so I think with some practice this would be less of an issue. The depth of field is so shallow, if you get the eyes in focus the skin looks very soft, probably because it's partially out of focus. Click on the images to see them up close. The Rokinon seemed to be a bit sharper but I was shooting it at f2. The Rokinon is a manual focus lens and it was extremely difficult to get the eyes to be sharp. I had a ton of images that were out of focus. On the rare occasions when I did get the focus right, the images look amazing.
The Canon would obviously be the better lens but it costs nearly $1900 while the Rokinon is only about $269. I also tested the Nocticron for my Panasonic GH4 and I found this lens to be the easiest to use. The images were always in focus and sharp with nice bokeh. This lens also has image stabilization so it really does well in low light. I only tested this lens in a dark hall so the images are terrible (shot at ISO 3200) but I think you can see this lens is pretty amazing as it should be since it costs around $1400.