While I generally agree that you'll save a lot of money buy building an AR-15 yourself, not everyone is so inclined, so skilled, or so outfitted to do so.
To speak directly to the OP question, of the two, I would speak very highly of the Bushmaster Varminter Special (in stainless). I have built dozens of AR-15's over the years, and the Bushmaster Varminter Special is the only factory AR-15 left in my stable.
I personally wouldn't use a .223rem for coons, but to each his own I guess. But then again, it's hard for me to think outside my paradigm, since I've been running coon hounds for 20yrs, and can't imagine shooting coons with anything but a .22lr.
But for coyotes out to 600yrds, it's hard to argue with a Bushy Varminter.