The original Chrome "speed nuts" (available from Pinball Resource) should only be used on the Gottlieb post screws which don't have any factory thread. Only the thread the nut cuts on its own. In this case, they do not need to be tightened against the plastics. If they are loose, either replace them or in extreme cases, replace the worn post screw. But the kind you can buy at the local hardware store are designed for threaded post and must be tightened down and therefore should not be used.
The nylon nuts can be used without tightening them down unless they are worn and then should be replaced.
Metal Nylok nuts can be used but often need to be tightened too low in order for the nylon to grab and will therefore usually result in broken plastics.
For the home, the Rubber caps are probably best. But are notorious for causing ball jams on routed games.