quad shots, and delts, are the easiest for me. with quad shots, the quad is right there in front of you. no contorting, you can use both hands to aspirate and hold the needle steady. but, with quads, you're more likely to hit a vein vs glutes so aspiration is mandatory.
also, when shooting quads you can hit and or inject into or close to a nerve and that is very painful. it's an intense, dull pain accompanied by severe burning at the site. you'll know you hit a nerve and not a vein as there will be no black and blue mark at the site but, rather, a reddish rash-type spot. afterwards, you'll feel like you got whacked with a baseball bat but the pain will go away in 2-3 days. it doesn't happen often but on the rare occasion it does, be ready for it and don't freak. just pull out the needle and re-inject elswhere.
the other thing is that sometimes when you inject quads, the needle goes past nerves, very closely. this creates a funny, tingly, slightly uncomfortable sensation that can put you off. just be aware of what's going on and don't freak out about it. still, even with these caveats, the quad shots, imho, are the way to go.
