I like any material that is durable and suited to the use of the knife, ie.- ?? display type art knife or is it a hard-core bash-em-up user ??
My favourite for a using knife is bead blasted contoured canvas Micarta above all else, but some really tough woods also do well. Most are stabilised but the inland Australian timbers, rosewood-family (Kingwood, Rosewood, African Blackwood) make awesome handles for hard use. Stabilised bone is also very tough. Regardless of the material, the handle needs to be comfortable to use and secure in the hand during use.
My favourite for a display type knife is still some super-exotic wood. I like the design to be very clean. 416SS bolsters and fittings can make the difference.