I've owned all three of them and found them to be quite different, although by far not as different as say the Planar compared to a Sonnar or a Biogon.
The most obvious difference between the three is the bokeh. This is a subjective issue, obviously, so ideally you'd have to find out for yourself. Me personally, in terms of bokeh, I would rank these lenses ('worst' to best): (1) Contax 645, (2) Rolleiflex 2.8, (3) Hasselblad 80 (version irrelevant, CB excluded).
Sharpness wise my ranking would be (worse to better): (1) Contax 645, (2) Rolleiflex 2.8, (3) Hasselblad 80. Oops, that's the same order ;-)
I never liked the 80 f/2 for the Contax 645. Perhaps the extra stop compromises the results, or maybe it is just me. Also, the Contax is 6x4.5 only, which may make a difference perception wise.
Overall, the Hasselblad and the Rolleiflex 2.8 are very close, if not on top of each other. I like most the Rolleiflex 3.5F, which is not on your list, unfortunately. Consider that camera, or some earlier 6-element version. In 6x6, depth of field is shallow enough to get good subject isolation even at f/5.6 or f/8. Planars 3.5 tend to be a lot cheaper than the 2.8 versions, and the same goes for the accessories.
I currently own the Hasselblad Planar and the 3.5F Planar. Both are wonderful, in all respects.