I've always used 25ga 5/8', 1", and 1.5" and rotate as others have stated. Left cheek, right cheek, left pec, right pec, left shoulder, right shoulder, left quad, right quad, left tricep, right tricep. (I've also tried traps and calves without pleasant results) After 20 yrs or so of doing this, I don't have any major scar tissue problems...