AR. Partly because of the accuracy advantage, but mostly because of the modularity. It's insane what you can build from a simple AR lower. Anywhere from a long-range rifle with a .50 BMG upper to an sbr for cqb and anywhere in between. Pick a caliber, 5.56, 9mm, 6.8 spc, .50 bmg, .22, 300 blk...the list goes on. It's truly amazing what you can do from that simple AR lower. I love AK's but if I had to pick just one, an AR would be it.