Magpul MBUS all the way for me. I do use a troy flip up front site on one AR, but thats just because the site is really close to my muzzle brake and it gets cooked (just a little bit )
http://kitup.military.com/2012/07/back-up-iron-sight-drop-test.html
http://vuurwapenblog.com/2012/07/08/buisoptic-drop-test/
http://kitup.military.com/2012/07/back-up-iron-sight-drop-test.html
http://vuurwapenblog.com/2012/07/08/buisoptic-drop-test/