I'd be concerned about long term availability of 300 BO ammo, let's face it it's most likely to run it's course as a specialty/fad round and in the future you'll be hard pressed to find factory ammo for it. .223/5.56, so long as you can legally purchase factory ammo you'll find it.
No round is ideal and IMHO at in the house distances I would expect for all intents and purposes that the 5.56 and 300 BO will be about equal.
I can't see a 300 BO unless you're planning to run it suppressed with heavy for caliber bullets.
I gotta disagree with all three of those points.
The 300 Blk is still growing in popularity, and doesn't appear to be going anywhere soon. Even if it did, you make your own from 223 brass and 30 cal bullets; two of the most common reloading supplies in this country.
The 5.56 and 300 do not perform similarly. High velocity light bullets vs lower velocity heavier bullets.
Subsonic 300 Blk is about one of the poorest choices you could make for defense, especially using the commercial 220gr stuff, which doesn't tend to expand or upset much. It's not a rifle round at that point, just a mild pistol round with really poor terminal performance, except for a few boutique bullet choices. You'd be better off just using a 45 or 9mm with good bullets.
