I started on quads because it is the only way I can properly aspirate. I have injeted hundreds of times and hit a vein recently. No fun, I felt like crap. If you stretch out your leg while sitting and place it over your other leg, it is actually an easy shot. First time I tried, I did it sitting down and it stung like crazy. I couldn't even break the skin. A bro on this site gave me the above advice and it is painless.