I either use Chris Lilly's pork shoulder or peach pork butt rub recipes if injecting, since they're both good and don't have quite as much salt. Don't have my "non-injecting" rub recipe handy, but other than salt and the usual spices, I feel dark b. sugar and a tad of cumin and Old Bay really help. Different strokes, but thus far, I've been disappointed with commercial rubs for pork butt, probably because most don't have enough chili powder or cumin.