RE: What size of peep?
 

Depends if you're a hunter or not? If you're a hunter, big! 1/4" is what I use as the larger they are, the more light you'll get in dawn and dusk hunting situations.

RE: What size of peep?
 

I use whatever peep size makes it easier to line up my shot. It doesn't matter if I am in the range or the woods.