I don't own a case cracker, yet the number of compacts I've opened is certainly a three digit figure by now.

There is no real rhyme or reason to Macs that are more stubborn than others aside from manufacturing. Model and country of origin do not matter. However, any Mac with slightly bent edges around the rear bucket will be harder to open. I have a badly bent Classic which requires a lot of strength to open.

My preferred surface is berber carpet. If it's a Mac I'm concerned about in terms of cosmetic condition, I'll throw down an extra towel for protection (usually just a regular bath towel).