i have the 135f2. optically it's the best lens i own and one of the best in the entire line up.
the 135f2 is long even on a fullframe (guess you know that already) and is of little use indoors. outdoors it is a very nice length.
i'm at work at the moment so don't have access to a great many samples, but bokeh and sharpness are amazing, even wide open:
100% crop:
but here is the rub:
although i don't think i could ever part with it (it's on my camera right now) i actually use my 70-200 f2.8 much more. even though the zoom is a stop slower, dof isn't all that much different at portrait distances so you'll still get most of the dreamy effect you want and bokeh is lovely and smooth too.
so it comes to this:
is the 135 f2 a great lens? yes, it's amazing. it's very sharp across the frame wide open, unbelievable at f4 and colour/contrast probably doesn't get any better. but...
the 70-200 f2.8 not only covers 135, it covers 85 too, so your most popular portrait lengths in one lens, which is also very sharp and has great colour/contrast too. maybe not quite as good if your pixel peeping but still excellent.
if it was me, as much as it troubles me to say it, i think the 70-200 f2.8 is probably the best value for money option and the most flexible for what you want to do.