I was in the same predicament as you at one point and went with an AR build for a few reasons.
I started my search with the FNAR. Great rifle, sub moa accuracy from the box and piston operated. People will say it's a PITA to take apart but with anything, once you do it, you'll get used to it and it won't be an issue. I'm sure it is difficult until you figure out the tricks.
The only reason I did not purchase the FNAR was simply because of the magazine cost. You are looking at 40 dollars or more per magazine. I like to have at least 10 magazines loaded up for the go. I'm not willing to pay 400 dollars for magazines.
The AR 10 is your next option. If you're getting a battle rifle you're looking for a quality rifle that won't fail. I've read too many mixed reviews about manufacturer pre built AR10 rifles that I just didn't feel comfortable buying one. I looked into build costs and it was looking too expensive to get a quality build for my budget.
If I had the budget I'd get an M1A.
I ended up building a sub MOA AR 15 that I'm more than happy with. It's my go to rifle for a few reasons. Widely used caliber and cheap(er) ammo. Replacement parts are readily available and magazines are cheap cheap cheap. I wanted to keep it as light as possible since it's my go to rifle.