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.
I can't speak from experience but I can easily understand why a 1/8" or larger peep would be best for hunting, especially in dim light. But for target shooting the smallest aperture you can use comfortably is best, because the smaller the hole the better your eye focuses on the target image.
The ideal peep aperture is one that closely encircles your scope body. You don't want the scope body floating around within a wide peep aperture, and you don't want a tiny aperture floating around the scope lens within the scope body.
If you don't want to buy a bunch of peepsights to find out which one fits you best, get a 1/16" Fletcher Tru-Peep. If it's too small, wrap some tape around the shank of a (sharp) 1/8" drill bit and work it by hand (don't use a drill) to enlarge the hole. Then use candle smoke or a marker pen to blacken the bored hole.
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