IMO, the TLDR for your use-case is to find a loading of Sierra Tipped Match King, commonly referred to as TMK. (Note, this is different from Sierra SMK which is similar). It is loaded by several manufacturers including Black Hills and Corbon. The TMK is a fragmenting round with a great reputation for terminal effectiveness, and will have likely the least amount of penetration concerns.
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The difference between 5.56/.223 ammo at urban distances is negligible. So I wouldn’t worry about that aspect.
You MUST realize, however, that anything you fire that is capable of stopping an intruder will go through several sheets of drywall and remain lethal. This counts for handgun, rifle, shotgun. An AR15 5.56/.223 round will go through less walls than say a handgun round, a true rifle round like .308, or a shotgun slug it WILL still go through some walls.
In something like an apartment setting, the BEST way to mitigate those concerns is to plan ahead. What are the possible entrypoints for an intruder, where might you be, and what angles/lanes can you fire through with a minimal risk of penetration. Know where your backstops are more than just drywall. Like some of the outer walls of an apartment may be concrete, maybe a bookshelf or other large furniture would work as a backstop. Also knowing the layout of any neighboring apartments would help too if you know this angle ends up going into the neighbors closet for example.
And it should go without saying, that the best way to prevent a miss going through walls into a neighbor is to hit your intended target. So anything you can do to improve your own accuracy (and a long-gun is a great start) will pay more dividends than anything else.
The only way to ensure it won’t go through any drywall is a shotgun with birdshot (which is NOT a reliable stopper) or something like Byrna pepper-ball shooter.
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