I think it depends on what sight you're using, and your personal preferences. I use a medimun size on one bow with a crosshair type sight, and a large for the bow with Trophy Ridge sight because, as mentioned, it "rings" my sight. Available light is a consideration also. Generally speaking, the smaller apature will be more accurate because there's less margin for error, but it's probably not the best choice for hunting. If you just disipline yourself to keep your pin in the CENTER of the peep, a larger peep will be fine.