I was just running some numbers through my ballistic calc for the AR with a 55gr bullet at 3000fps. IMHO If you want the best zero for home defense , the 100yd zero is best . Like what was said above . There is NO way to make up for your barrel being below the optic or sights with said sight . No matter where your zero is the bullet will leave the barrel 1.75" to 2" below the sights . Knowing this to be true a 100yd zero will be 1.75" low at the muzzle . dead on at 100yds and 1.75" low again at 175yds . That gives you an extreme spread of 1.75" all the way to 175yds . In contrast the 25yd zero would put you 3.5" high at 100yds with an extreme spread of 6" out to 300yds . A 25 foot zero would put you some where around 12" to 16" high at 100yds and the extreme spread would not even be worth talking about .
So it looks to me that for HD/SD the 100yd zero is best for your AR .
As of this date 8-18-14 at 6:42am I became a proud grandfather I guess I'm officially old