For a range plinker and at those ranges, there's nothing wrong with either choice. A 1x9 twist barrel will serve you well.
If I were choose between the 2, I'd go with RRA, I just don't like the Bambi roll mark fer Stags
Also RRA makes a nice 2 stage trigger you can add to you rifle at a minimal cost. If you plan on using this AR for more serious roles, I would consider other options.
Just keep in mind that, either company has models that are really close in price to much better ARs like the others have mentioned. You can get a Colt for under a grand, just the same price point that my LGS sells Stags for! Insane!