I think every injection site has its pros and cons :
glute : best for voluminous injections, no pain, low chance of hitting a vein/nerve, but very hard to reach for many people (especially those who are fairly big)
quad : easy to reach, second best site for voluminous inj., but much greater chance of hitting a vein/nerve
delts : medium/low chance of hitting a vein/nerve, no pain, but not good for inj. more than 2ml and they become harder to reach as your chest grows
biceps : huge chance of hitting a vein/nerve and great pain in the days that follow - i never shoot there
These are only my personal views based on what happens with my own body.