The collapsible FSU 50s--Industars 10, 22, and 50--are pretty good for their price, I think, but won't collapse full with the Bessa R. Still usable, though, just be careful with them. The other Industars--I 26, 50*, and 61--should also be fine on a Bessa. The Jupiter 50s-- J-3 and J-8 are potentially very good but the wider max aperture will mercilessly show any focus problems they may have. A correctly adjusted one is wonderful, I think. My main 50mm is a 1955 J-8.
The caveat with any FSU lens is that it might or might not focus correctly on a true Leica standard camera.
The J-12 will most often not work well with the Bessa. Either it will not mount fully or, as there is some variation, if it does mount OK, the rear element will block the meter on the Bessa. I like the J-12 and have a FED 4 camera so that I can use it.
That said, the easy choice, again I think, would be the Voigtlander Skopars. the 35 and 50 are really good and not too pricey.
Good hunting!
Rob
*there is a rigid I-50 as well as a collapsible.
PS: If you decide on FSU lenses, the important choice will be the seller. Find a good dealer who has a return policy.