25awg 1 1/2" for me! Take the amp or bottle and wrap it in a warm towel and the oil base will thin out . Then place a heating pad or warm towel in the inj site it will speed the dispersal of the oil base ,Also it gets your blood moving to and from the area more readily.
have done 23's and 25s at 1.5 " ... all the way in for glutes.. about and 1" for delts and quads. easier with quads, more control with both hands. 25's are a pain tho..