Over the years I have tried every variation of rubs, some with the entire pantry and others very simple. Long story short the rub is just on the surface and while it does add flavor it's just to the outside. You can get some in every bite depending on how you slice it. One rub I tried with coffee added was pretty dang good.
Really adding flavor bang for the buck you can't beat a brine. Most brines have salt and sugar but I consider the sugar and anything else as optional. Here's a link to a few examples. http://www.realsimple.com/food-recip...0100000091640/
Also, the cut of pork matters. A loin is very lean and needs some added flavor while a butt is fatty and tough requiring low and slow for along time which means any rub will burn off but the payoff in flavor is worth the time.
Lastly, you can use an injector. Anything you like. Tabasco and Malibu rum. Garlic butter. Root beer. Italian dressing. Best pork butt I ever made was injected with hot wing sauce and chuck it in the turkey fryer.