Which case for Nokia N95 do i buy, Leather case, silicone case, Hard case?

Probably a leather case is okay.

i think a hard case maybe fit your Nokia N95,
you can look at Slim Metal Case, it is made of anodized aircraft-grade aluminum prevents from scratches and damage
http://www.shopping-toys.com/aluminium-metal-black-super-slim-cover-case-for-nokia-n95-8gb-p-313.html