I think rotating a few places is the best course of action but I don't really give scarring any real concern, I think that that's a little overblown IMHO.
I inject my HcG into my thigh with a 31 gauge 1/2" insulin syringe. The area is about even with the apex of the crotch..in the middle of the thigh laterally. I pinch up some skin and inject into it at an angle then rub it a little after the injection. I inject my T into my delts with a 29 gauge 1/2" syringe. Both injections are literally painless.