Rub whatever you want, then just before placing the pork in the smoker lightly coat and rub in brown sugar.
What that does is, it will go from crystaline state to liquid and then that sugar will caramelize with heat encapsulating the meat just like an M & M. No, it doesn't change the meat to chocolate, but by encapsulating the meat it does help preserve the meats moisture and thats normally a good thing. Its not really too sweet.
Also if using a firebreather you'll need to maintain a lower smoking temp but its not like you are trying to crisp the skin like on fowl. Basically below 300 works good so the sugar cramalizes and doesn't burn.
Normally I am just salt and a pepper (Ancho is my favorite right now) maybe cayenne. Then a sugar rub down. If I feel like a wild man, add some garlic or onion.
I used to like Papricka (Ok, I know, thats why I had a secretary), till I figured out it can and does burn. But if smoking at a low temp, besides the taste, it gives a really nice color.