I've had two Zorki 4s and one 4K, and the worst I've had happen is the long shutter speeds be off. They're great cameras. I can't say the same about Feds or Kievs which have mostly been a bad bunch in my experience. The Zorki 4 is about as good as it gets in soviet rangefinders. It has a big, bright viewfinder, it's relatively easy to load, the quality is decent, and they made them for a long time so you don't have to gamble on a camera that's been abused for 75 years. But they also ceased production before Soviet quality went into the toilet in the 1980s (a late Fed 5B was by far the most poorly finished camera I've ever held, excluding some toy cameras made in Hong Kong, and later Kievs weren't much better). So you've got a good start in the 4.
The Leica LTM cameras are a step back, you get a smaller viewfinder which is useless for anybody who likes to compose their photos, and you get fiddly film loading. These are cameras for masochists and nostalgic fanatics.
The Canon rangefinders are a bit of a step up. They're finished better, you get a better viewfinder, and you get lever wind, and relatively simple film loading.
Beyond that, there's the Cosina line of LTM cameras, assuming you want the feel of a modern camera. I prefer old cameras.
