A difficult choice.
A difficult choice.
It would take forever and be highly subjective if all the various FSU cameras were contenders, as you can see by the avalanche of replies you got. , but I'll assume there is a reason why you limit to those specific ones.
The Fed 2 has the benefit of having the longest rangefinder base of all the Russian cameras, and also looks really cool. I think it's the prettiest one of the lot. The wide base rangefinder is a lot more precise than almost any FSU lens you will buy, so it's only really valuable if you take the trouble to adjust the lens's focusing mount. It's fairly easy, and there are instructions on this forum.
A Kiev 4 will take a line of lenses that were typically more accurately adjusted. In the case of the 50mm lens, the focusing mount is in the camera body. Typically the older the Kiev camera, the better the quality, so presuming you chose the Kiev 4 because you want the light meter, if at all possible you might look for an early Kiev 3A or better still a Kiev 3 if you can find one with a light meter still working..., and can live without flash sync.
The Zorki 6 is the latest model in the line, and has some modern features, but I'm sorry, it's just butt ugly, and I tend to think that the quality of FSU cameras generally got worse as the years passed.
I see you found a good deal on a Zorki 4. That's a good choice, with a good VF, flash sync and decent handling. If it's one of the newer ones with that horrible cloth covering, you can peel that off and get all artistic with leather from Tandy's. Watch out though, the later self-timer screws were LH thread and they break easily.
Jupiter 8's are really easy to find. I probably have a few more than I have any use for, so let me know if you can't find one.
Cheers,
Dez