If say you have 3cc of oil a week to inject and you have already injected in both glutes, both thighs do you inject like 1 1/2 cc in one calf/bicep/tricep then the other 1 1/2 in the other calf/bicep/tricep? Do you switch pins if you do that?
Your thighs and glutes can each accomodate having multiple sites. Just give yourself at least 2" of distance between sites so long as you stay within the safety zones.
If you only have 3cc of oil per week then glutes and delts should suffice and would be my preference. If you're comfy with quad shots then they're even better; not everyone is.
You could consider staggering your injections rather than doing all 3cc on one day, depending on what you're running.