Bone, bone, bone, bone, bone.
Nothing else lasts as long, nothing else works as good, nothing else sounds as good (not that it really matters much, as it only really effects the sound of the open strings, and only minorly).
Tusq is plastic. They can call it "sythetic ivory" all they want, but it looks like plastic and it wears like plastic. Besides, bone is better than REAL ivory, so why would I want to go with FAKE ivory.
Graphite is fine, if you use a trem a lot, but it will wear out really fast.
Bone, bone, bone, bone, bone.
Oh, and ask if they have unbleached bone. It is harder, so it sounds and wears better, and it has this cool streaky light brown stuff going through it that looks really cool. I don't really even stock bleached bone anymore.
Light
"Cowards can never be moral."
M.K. Gandhi