M4. An M16A2 type rifle is not a whole lot lighter or handier than the FAL for a whole lot less payload, as you no doubt already know.
I had a Colt CAR-15 in my latter LEO days for SHTF situations and it was just the ticket. For starters it was unique and evil looking in those days which is a very useful thing; and very compact and handy. Fast, too.
I sold it when I retired into sagebrush country where a 16" .223 is a bit silly. Even so I still have twinges of regret for selling it.
Still, my M1A is a comfort if something wicked this way comes.