I'd recommend mixing your injections sites up to include more than just your glutes. Scar tissue can become a
problem later down the road. Stick to the easiest areas to inject - glutes, delts.
If you choose to go with quad injections be careful because its pretty easy to hit a nerve, atleast I tend to
when injecting there as apposed to other places. I remember the first time I hit a nerve in my quad I
literally bent the needle slightly due to the rapid firing of the muscle. I'm not trying to scare
you away from them, just letting you know of possiblilities. I don't touch my quads anymore for other reasons, but some people love them for injections.
I'd say rotate by following a circular path from delts to glutes, meaning right delt, left delt, left glute, right glute, and then repeat.
By doing this you've effectively reduced the number of injections to your glutes by half. In the long run they will thank you.