If you look at the OP's post it's pretty clear that "all of the above" fit his needs and it comes down to personal preference. I go with more of a whatever's closest at hand theory. I've used 12ga's, .22's, .22M's, and centerfires in many configurations for the task he has at hand. All work. Sorry John, but your recommendation of a single shot is lame. I've hit coyotes and about every critters around with 1st shot, 5th shot and everything in between. If I have something that needs killin around the place, good shot or not, I'm pullin the trigger till it's down or outta sight.
But the OP requested semi auto .223 so take your pick, it's not brain science. Do I have a personal preference within his specs? Hell yes, a stainless Mini Ranch. But I ain't gonna turn down an AR either. If I toss his specs out I'll revert to Art's post and add lever actions in whatever cartridge you prefer including the rimfire magnums.
LK