Let's see -- the IIc is an unmetered version of the IIIc, and has the 45/2.8 Xenar, a Tessar design like the Color-Skopar -- slower than the Xenon (or Heligon you sometimes can find), but actually the Xenar has the reputation of being sharper. So the Xenar and Color-Skopar are directly comparable, though the Xenar is faster.
The IIc does have a nice coupled rangefinder, and lever wind, neither of which the Vito has. I think you have to get to the Vito III to find a coupled RF -- and that's a superb camera but pricey. The Retina is as a result a little bulkier and heavier than the Vito, but I think it's worth it. Yes, the Retina has the cocking rack issue, but replacement cocking racks are available and I think it's not that hard a job to replace, particularly with a nonmetered camera like the IIc.
Here's another suggestion -- the Zeiss Ikon Contessa folder. Great camera -- a little "fiddlier" than the Retina but quality throughout.