I have a Mamiya C220F and a C220 + 55, 80 and 180mm Super lenses. I also have a Rolleiflex 3.5F with Planar lens. I also have one inherited Ikoflex and also a Flexaret, which I never use.
Rolleiflex is more compact and also better ergonomically than the C220/C220F and the Planar is a sharper lens than the Mamiya-Sekor 80mm. I also like the slightly wider angle of the 75mm Planar better than the 80mm Sekor (remember also that the Rolleiflex 2.8F has 80mm and the 3.5F has 75mm lens). C220F has a brighter finder, though. The interchangeable lenses are of course a big plus, the 55mm is a very good lens. The 180 is a little awkward to use handheld, at least at shorter distances.
The Ikoflex is still capable of producing nice sharp pictures when stepped down to F8 or F11, but the viewfinder in mine at least is very dim, the mirror should be resilvered I guess.
My verdict:
if you can do with one focal lenght and can afford it, get a Rolleiflex 3.5F and if you are on a tighter budget, a Rolleiflex T or a Rolleicord.
if you want interchangeable lenses you have but one option, the Mamiya. I would recommend the C220F or the C330S, because they are the newest models.
If you don't mind carrying stuff, get a C220F + 55 + 180mm lenses AND a Rolleiflex 3.5F, then you got the best of both worlds =)