I've owned the 85/1.8 and currently own the 85/1.2L II.
If your goal is portraiture, but you can't deal with secondary spectrum/longitudinal chromatic aberration/magenta-green fringing/spherochromatism/etc., then I don't recommend either 85mm lens shot wide open. The 85L is much better once stopped down to f/2 or so, but at f/1.2, it's going to give wicked color fringing in areas of high contrast. With the 85/1.8, the fringing is still there as well.
The 135/2L is a better choice for avoiding this specific aberration, and the quality of blur is very, very nice. I would say that it's as good a portrait lens as the 85L. It's also more affordable. I decided it didn't fit in my lineup because of the other lenses I already own, but it is an extremely well-regarded lens, and in my opinion, for what you are looking for, I think it fits your criteria best.
What the 85L (and 50/1.2L) can do, however, is retain strong background blur while giving a wider angle of view than the 135L. That's why those lenses are so coveted--they are capable of giving a certain look that other lenses cannot match (but it takes a particular sort of composition to reveal it). The trick to using these ultra-fast aperture lenses with a lot of color fringing wide open is to shoot in conditions that are low-contrast, with few bright highlights. The 85L is not a lens that works well if shot wide open in direct sun.