Egad, complicated issues.
Ok, the BEST leaf switches are the kind that were in the original Wico leaf joys (Ok, technically the BEST ones are in pinball targets, but anyway). The worst ones I have seen are integrated (non-removable) into the holder, and don't have a true "contact" just a raised dimple on the leaf itself.
Now for the good news, none of this matters when it comes to home use. The fact is that you simply aren't going to wear out your new leaf switches on a home use machine.
So basically my advice is to order away, and use any vendor you would like.
Also (I may be wrong on this), but I believe the plastic/nylon ones are for joysticks and the fiberboard ones are for buttons, or the fiberboard ones might be for pinball applications, you might want to ask bob. I myself would probably just order the complete sets from whatever vendor I wanted to use, I seem to recall someplace having nice translucent sets for like $3 each.