I have always like the addition of the slip on kind. I have long arms, so I need a long length of pull. Most of the firearms that I have are collectible, so I don't want to drill into the stock either.

I use a slip on with an extra inch of closed cell foam cut to the profile of the stock inside it. It makes it just an inch longer, gives me more recoil absorbtion and fits my arm length well. When I put it on any Russian gun I have to put 2 of my spacers inside it, they must all have very short arms!

In any case, you can also cut 1/2 of the rubber skirt off of the slip on ones. It is too much interferes with my cheek weld and isn't needed to keep the pad on the butt.