Quads are tricky for me. I went too deep once, and hit a vein, and caused a huge painful hematoma in the deep muscle. It took over a month to clear out. I do delts with anything 2cc & less (I have fairly thick delts, so no problem for me, but thinner delts might not work as well). Glutes are the most popular spot, but if you have trouble reaching, and you don't have a buddy to do it for you, I'd keep using quads with a 1" needle (or even 3/4" if you have zero fat layer on the quads). There is only a small area on the side of the glute, where you can inject. Do a search for spot injections (this site), and there is more good info there.
Charles