I personally use the medium sized peep. It's latrge enough to let in light and not so large that it is ineffective. The diameter is such that I can see the outside of my pin housing and no more. Perfect. To address low light conditions, I use a light, which came with my sight. For sights that don't come with a light, you can either purchase the optional light made for that sight or you can get one of those lights, I can't remember the name, that's long and has adhesive backing on it. It usually sells for around $8.00

Also, when getting your peep adjusted, a good tech will help you figure out the best spot, by making you close you eyes. Since you're new, your anchor point may not come naturally. If that's the case, the bow tech should have you close your eyes, when you pull your bow back, to set the peep. When you open them tell the tech if the peep needs to move higher or lower. He should have you let down and rest a second and then do it again. He should do this several times just to make sure you're set and not moving your anchor pont; which will cause the peep to be directly out of your line of sight.