I've killed deer with both and IMO, were pretty similar designs.

I now shoot the Impact Cosmic XL
I can't remember the name of the Cosmic I had, but it was a moveable single pin sight, all metal, very similar desing to the Cosmic and about the same price.

I choose impace b/c I like the clear aperture and b/c I have contacted their customer service several times and they have helped me out. I just ordered the crosshair aperture to try with my Cosmic frame. I hope to start shooting soon and find out which one I like best.

I don't use either but have looked at both extensively. In fact I see them every day at the store. Were it my choice I'd take the Sidewinder simply because of the metal pin guard vs. molded plastic. It'll be stronger in the event you decide to throw your bow through the woods after you miss---or just do something dumb and drop it out of a tree. The fact that it's made of all machined aluminum is a plus IMO. To my way of thinking it costs more to machine a piece of aluminum than it does to mold something out of plastic--and the Sidewinder is about $20 cheaper. How did that happen?

My hunting sight cost $100+ so that says it's not a money issue, that's for sure. I just look at value for the buck.

Oh, and I'd take the three pin model.