I have done with and without many times and I can honestly tell you the injection is better, you get a totally different taste on the inside.
I tweak the rub as follows though:
1/8 cup dark brown sugar
1/8 cup white sugar
1/8 cup garlic salt
1/3 cup kosher salt
2 Tablespoon chili powder
1 teaspoon oregano
1 teaspoon cayenne pepper
1 teaspoon ground cumin
1 teaspoon black pepper
1 teaspoon gran onion