I have had rifles in both .284 and 280AI. Both are very solid performers. All things being equal, with a long action, I would vote for the 280AI. The brass is easier to come by (or make) and there is a lot of load data for different weights of bullets which gives you a more versatile cartridge. Of course, if you weren't really thinking of hunting anything larger than deer, the .284 is almost perfect. But again, for larger, more aerodynamic bullets and the ability to shoot long range, the 280AI is the better choice.