I wonder how many more times we're going to get this "which one is best" question. And every time it comes up, there are a whole string of answers, none of which really answers the question. They are all personal opinions.
I have to agree that the seller is probably as important as the camera. There seems to be general agreement that it's hard to beat Fedka, and my own experience bears that out. Yuri may be more expensive than some of the foreign guys, but he's also probably more dependable.
Also, the "which one" question usually asks FED/Zorki or Kiev, so it usually eliminates the "other" one. I have several of both, mostly different models of each brand. And I also seem to feel that the Zorkis are better made than the FEDs, but I have more Zorkis, so that may influence the feeling.
Whether or not a given camera is worth paying for CLA has to be an individual decision, since we all have our priorities when it comes to values. And given that we're talking mostly about cameras and lenses made 40-50 years ago (or more), resurrecting an old camera is a personal choice.