The Nikon would be way more versatile due to the entire system but if you needed to travel light may not be the right answer.
Bodies are about the same weight. I got my F for $25 then sold my M3 for $800. Then I bought a light Voigtlander pancake 40/2 lens for my F. A nice light kit, plus I can still swing it a deadly weapon if needed. (Don't laugh I have seen it done with an F) hehe.
I'd pick the Nikon F if I wanted more capability/versatility and speedier operation. I'd pick the M3 if I wanted to carry a small package. Both are high quality cameras and both companies made high quality optics, so those things would be the least of my concerns.
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