I have never used a store bought rub.
I usually go as far as to grind my own spices as I am making the rub.
What I use will depend on the meat or veggie being cooked, but I have several "go to" spices that the rubs are built around.
John - Sir Porkalot BBQ Team BLUE Thermapen
*Stickburner (horizontal offset)*Weber Performer*Baby WSM (14.5")*Various Weber Kettles*Cast Iron Cue-Grill (restored '60s era grill)