Quads. I inject the upper outer quad, where the tissue is somewhat softer and more pliable than further down the muscle. With quads included, you'll have 6 sites to rotate through, which should be enough. Next I would look at lats, if you have enough muscle to inject into them. The bigger the muscle, the more room oil has to "spread out". In something like a delt or a bicep, it can only spread so far and often the smaller muscles get more irritated, so watch those delt shots.