I agree with Dralowid. Pre-war bodies are more hand-made and better quality, although not by much. The post-war ones make better users, late ones have a single-piece cast chassis so they're a bit stronger (Leica also made that step) and they will take most LTM lenses.
If you buy a pre-war one you may or may not get lucky on the mount-registration and thread. Pre-war examples are, in effect, a fixed-lens camera unless you can pick up the pre-war lenses and have them adjusted for the body. Neither practical nor cheap!
The very late examples of the FED 1 also have very thin film guide-rails, which can mean your film slips out of them (mine does this). At worst, you'll get some slightly skewed frames and sprocket holes in your picture. You just need to put in a spacer to raise a modern film cassette up to stop it