Get the .223!
To shoot inside winter time get a .22Lr conversion and get back to .223 after.
At least you will have some fun at 200 yards + ranges whit it.
I think 9mm AR's are useless. IMHO!
Yea cheap ammo but no recoil ( Since no recoil why you don't just go for a 22 instead?!? ) and not what it takes for long range shooting fun.
Cheers.