Use my 930 SPX for a quick 8 shot semi-auto close in clearing and then pick up the 30 rd AR or AK......
Specific to the question: 556 hands down. Target rich environment, longer ranges, and the need to penetrate potentially (door, window, car window...).
You might not have the option of staying in place.
Today even many of the bad guys have body armor.
In normal home defense over penetration is a concern, but in a war zone you want that! I want to be able to shoot someone standing behind a door, I want to have the ability to penetrate some body armor, I want to be able to shoot someone in a car (effectively)...