Rifles tend to not be the best gun for HD due to overpenetration. If you live away from other people (no one else in the house too) this is not that big of a problem. You did pick probably the 2 best rifles for HD though.
The AK offers rugged dependability, with a round that has more punch then the .223. They are awesome guns, and tend to not be picky about what you put through them.
The AR offers a easily customized platform that has proven itself. They do have to be really clean to ensure that they always go bang.
Either way, you can't go wrong. Both the 7.62x39mm and the .223 are man stopping rounds (though, you might have trouble finding hollow point 7.62 locally depending on where you live). The AK is usually half the price of the AR. I would do what unclebear and primer1 said and hold both of them first to see what you are comfortable with.
PS. They both shoot cheap ammo, and are a blast at the range.
Personally, I would go with a 12 ga for HD (My fav is the 870). Look at the Saiga 12 ga. It is a 12 ga AK!!!