Quads are way mire painful to inject, and cause way more irritation post injection. The swelling in your quad can make it feel like someone gave you a dead leg for 2 days (that means feels like someone hit you so hard in the quad that the muscle doesnt want to move nornally)
I prefer ass, and occasionally delts. I do quads RARELY, even though I pin 3x weekly. (I use almost all short esthers)