Both calibers will kill deer without a problem. If I picked the AR, the bullet I would try would depend on the twist of the barrel. For a 1 in 7 twist, I'd try out the 70gr Barnes. For a 1 in 9 twist, I'd first look at the 60gr Partition. Their are others that will work just as well, but that's where I would start. I generally use 30cal rifles, along with a .35 and 444 on occasion. I also hunt in the Southeast and unless I'm hunting on a field, most of my shots are inside 100y. I suggest pick the caliber you want to hunt with this season, then PRACTICE a lot. Practice with a rest, free hand, right hand, left hand, prone....... I watched a 12 year old kill a nice buck at 256yds last year with a 223, his Daddy had him shooting all summer out to 300yds. He made a perfect shot and deer went ~60yds. I wouldn't worry much about what caliber to pick, just worry about becoming very proficient with one I picked.