I use mostly hickory, followed by pecan.
I have a lot of hickory trees on my property. I collect the nuts and let keep them in a bucket. When ready to smoke I soak them in water the same as I do with the wood chips, the oil in the nuts makes a richer smoke. I have 2 big green eggs and cook for family events a lot, pork butts for 12-14 hours with hickory nuts is pretty darn good.
I also throw a few chips of hickory on the grill when grilling rib-eyes, just a touch of hickory along with the char-grilled flavor makes it just right.