Used both on my machines and found the felt is a good cheap option for some of my B titles that I don't wont any more damage done to.
I use the plastic ones on my cookie cutlers as they just finish the cab off after it has been re decal.You can trim the felt ones, but the plastic do look nice.Black the best ,seams to go well with any cab.

Most of the time, damage is done by the legs not been tight and the machine moving back and forth during game play or dragging the machine on the floor to move it.
Check your brackets inside the machine and make sure all the locking screws are there.Found a few machine without them, causing the bracket to move on the inside of cabinet.

Tight, but don't over do it as it will mark the cab.