I do both. My wife does the glutes and I do the quads. Rotating 4 spots makes it one injection per month in the same muscle.
So far so good.
Does it hurt injecting in the quad? Does it affect the test absorbtion?
It's been pretty much pain free. I prefer the glutes, but it's not really that much difference compared to quads. As far as I can tell, absorbtion and how I feel is not any different between the 2 sites. I also use a 25ga 1" needle... seems to be the overall favorite choice amongst self injectors.
The quads are by far the easiest to get to if doing it yourself.