I'm with Jon, but I'd do both. There are flavors that develop when the rub cooks. I'd use a finishing sauce to even texture and moisture but the targeted flavors would come from the sauce in this case.
"Taco seasoning" is an American invention. It's (in varying proportions), chili powder, onion, garlic, cumin, Mexican oregano, something for a little heat (crushed red, cayenne). Build a rub from there, adding some sugar. Salt the meat first, apply the rub over the salt when it draws moisture.
Consider: 3 parts chili powder, 2 parts onion, 2 parts sugar, 1 part garlic, .5 part oregano, .5 part cumin, .25 part heat; blend then remove a little, say, 1/4 tsp, sprinkle a little salt on it and taste. Adjust from there.
Make enough to flavor the sauce(s) you make.