I've done both...45 is less painful going in....I think as long as it ends up int he muscle its still ok...do check 2Thick's site though for proper injection site on the shoulder..
Straight in at a 90 degree angle is good, I use a 1" orange pin all the way in, you have to get some one to shoot it for you though, especially if its a thick depot test or primo.
If IM which most AS is designed for, then 90. The 45 is better for SubQ. Should say IM on it. Trust me on this, it is what they teach in every medical related school and I have given thousands of shots... not just on myself. ;-)