Most of us here are gun guys. What we might ADD as another rifle, or might recommend as an only rifle if we had only one is quite likely different than what really makes sense for a guy who really only wants one rifle. If I think about a first rifle, as opposed to an ONLY rifle, that might change my manner of thinking.

For a one rifle guy, do not get anything "exotic" like 6.5-284. Great cartridge, but not great for someone who doesn't reload. The 7-08 is a great option, but so is .243win or .308win. So are 270 and 30-06. If it isn't on the shelf at Walmart, take a pass - not that he'll buy it there, but rather use that standard as your reference for determining common popularity. If he can't find it, he can't shoot it.

Avoid heavier caliber cartridges simply because this guy might not shoot as often, nor have as structurally sound fundamentals as a more avid shooter. If he's just punching paper at 200yrds or less, a 223rem is great. If he's thinking farther, grab a 243win or 7-08.

Personally, I'd lean heavy towards .243win.