Obviously singled out was the clear winner but not that practical for every day killing. steady aim was very effective though.
Single Out is actually great for everyday killing, it's highly underrated.
My thoughts on it here. The tl;dr is that it greatly speeds up the toughest fights (it's a 40% DPS buff against isolated targets with my particular stats) and the toughest fights make up a disproportionate amount of your time unless you're playing at a faceroll difficulty. It's a regular on my bar.