Shopping around for an ar-15?

I would go with flip up rear sights. Is this for home defense? If so, the holographic sight is a good choice. odds are it will not clear your front sight post if you are looking through your rear peep sight. the dot will end up on top of your front sight post if zero is good. If you are thinking about competing then go with an acog. Some have a holo sight as well. More $ though.