My favorite pork butt rub:
Amazing Ribs Memphis Dust.
3/4 cup firmly packed dark brown sugar
3/4 cup white sugar
1/2 cup American paprika
1/4 cup garlic powder
2 tablespoons ground black pepper
2 tablespoons ground ginger powder
2 tablespoons onion powder
2 teaspoons rosemary powder
I apply salt the night before, then in the morning while smoker is getting hot, I apply a light coat of mustard as a "glue" to hold the rub, and apply memphis dust pretty generously.
My usual internal finish temp target is anywhere around 200F-203F... I shoot for around 250F-275F for the smoker.
Once it hits finish temp, I'll wrap it in foil and hold it off the heat for about an hour before pulling.