For sheer bokeh, it's hard to beat the 135L wide open, particularly on full frame such as your 5DII...
Sabrina - lost in thought
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EF 135mm f2L lens at f2.0. EOS 5D Mark II camera at ISO 6400, 1/200 shutter speed, handheld, available light.
Note that the 135L is an older design and it doesn't use curved aperture blades. So stopped down at all you can see the shape of the 8-bladed aperture.
All the 70-200s use curved aperture blades that somewhat enhance their bokeh when stopped down at all.
On the other hand, I'd much rather shoot portraits with the 135mm. It's a full stop faster than the fastest f2.8 zoom, two stops faster than your f4. It's smaller, black and less intimidating than any of the 70-200s, too.
The 135mm also works quite well with 1.4X teleconverter, giving a nice 189mm f2.8 (though without IS). And it's fast and close focusing. Works well with macro extension tubes, too.
It's a personal preference, but I consider the 135mm a "must have" lens on FF. Personally I bought it along with my 5DII. It's quite good on crop, too, but I resisted buying it for years while only shooting with croppers. Then when I finally added full frame to my kit, it was the first lens I added.