Like so many other things we smoke it becomes a personal choice.
My personal favorite is hickory, but I like a stronger smoke.
Maple is very good fer sausage, I use alot of it, most a my customers prefer the maple, a nice smoke with a hint of sweet to it.
Any of the smokin woods will work, some will be very mild, apple is nice, but dosen't give much flavour ta things like summer sausage, but if it be what ya got will work.
Ya can also do some wood blends, hickory an maple make up a nice mixture as well.