Console scrub here.
I keep it on. There were times back in CoD BlOps where I TRIED to play it without autoaim, which as a sniper, will fuck you over more often than it will help you. But that was also during a time in Blops history where they were tweaking the controls every other week, and every time they did, I had to get used to sniping again, and said fuck it and put aim assist back on. And then there were times in Blops where the aim assist is so god damn strong, that I can't actually MOVE my aiming reticule off of a moving target if he moves past another one.
In single player games, I'll turn it off if I notice an option, because it's less important there, but consoles, no. Not anymore. I haven't played shooters online though with any sort of regularity for years though, been mostly CoD/BF free the last while, with Titanfall being the only other shooter I spent a lot of time with in the last year. Picked up BF Hardline though, and the aim assist that I've noticed is minor (while I've been sniping at least.) It has a weak pull so I've never had to shove my stick in the opposite direction if I changed my mind on if I want to try shooting that person or not, unlike CoD which just decides, "Oh, you wanna look at this guy? LET ME HELP YOU WITH THAT *takes controller out of your hands*"
I doubt I'll ever take aim assist off as long as I'm on a console, because of that very reason. Everyone on a console will have aim assist on in a shooter, not gonna deny myself an advantage that the game itself is giving me and everyone else, no matter how small it is.
As for my overall preformance in shooters? Meh, usually changes depending on my focus for the game/match. I love sniping, so in general, I try to stay away from the action while looking for my shots. I'd put myself in the "average" category, maybe slightly above average when I found my ideal class setup.