There are many choices when it comes to a rangefinder camera for your FSU lenses. The Leica III series are wonderful, they have far better fit and finish than the old FSU cameras (I own an FED S, and an original '48 FED/Zorki), and are much smoother in operation. I had Oleg rebuild my FSU cameras, and though they are in perfect working order, they simply don't match my old Leica IIIA or IIIF in smoothness. The ultimate III is the IIIG, which runs about the same price as an M body nowadays, but which looks quite nice with FSU lenses on it.
Leica M cameras are a completely different animal compared to the Barnacks. They are solidly made, fill the hands just right, and the viewfinders are superb, especially the focusing patch. But, they are not cheap, unless you get lucky and come across one at a thrift store.