Actually, something no one ever brings up is that the length of the needle depends partly on the size of your quad. If you are skinny 5/8 might be ok, but that's kind of small. I recommend 1" and 23 or 24g.
i'm using a 1" 25g for injecting my quads and and glutes (2cc's eq in quads and 2cc's eq and 1 cc enth in glutes). it's a slow inject like gladiator said but that's better for you anyway. i would say get at least 1" pinz if you can.
if you have enough muscle on your quad burying it should be no problem...if not, just leave half an inch out or so. remember to push in slow so you know if you are coming close to a nerve.
I just shot it. I put it in about an 1" I was pushing it in slowly and started to feel it hit something but just gently push some more and it went away. Aspirated then shot. I like it better than the glute so far.
i like quads better than glutes too, way easier to administer to yourself. i've only done eq though in quads, some shit is supposed to hurt like a bitch when injecting into your quads. that's for the future though