Leica Ms and Nikon F#s of similar age are of equal quality to one another. They are different tools for different types of image making. That is all.
If you need to remember why you have an M3, just take it out of the bag and use it for a week.
My M2 is my primary camera for just about everything that doesn't happen in a studio, I've only owned it for just under a year, but I put my gear through a lot, and the VF is still as accurate as the day I got it.