I like to experiment quite a bit, so I don't really have general preference...it just depends what I'm in the mood for at the time, I guess.
I will say that with the base rub ingredients of cbp, garlic, chili powder, brown sugar and kosher salt, I find a blend of approx. 40% hickory, 30% mesquite and 30% cherry seems to have a nice balance for butts. A bit sharp from the hickory, some melding of the stronger flavors of certain parts of the shoulder with the mesquite, and a touch of sweetness from the cherry.
I don't have a wide variety of smoke woods available to me here...the above mentioned and apple is about it.
Hmm, saw 3montes post, then wondered: do you mean smoke wood or fuel wood?