7mm-08 would be my choice for deer amongst the many .308 configurations.

Any of the three cartridges you mentioned will do just fine. If you were to mix varmints in I'd lean towards the 243. For a strictly deer gun the 7mm 08, if you ever had plans on hunting anything bigger the 308. All three rounds can be found just about anywhere, though the 7mm not quite as common as the other two.

If this is his first hunting rifle, and you aren't planning to hunt anything bigger than "little deer", get the .243. It's the lightest recoiling of the three by a healthy margin making it much easier and more fun to shoot, and the deer aren't going to know the difference. As for the guy who said .308 ammo is easier to find and cheaper, I'd like to know where you shop. Every place I've ever been that sells ammo stocks .243's. And, I've never seen hunting rounds for .308 that were cheaper than comparable rounds for the .243. The only ammo I've seen that is cheaper for .308 is the military surplus stuff, and you can't hunt with that...

I shop for ammo for the range at the spots that carry the best deals, .. that would be Dunhams, D1ck's sporting goods, Meijers, Walmart ....RThose spots carry the vanilla brands at the cheapest prices ON OCCAISION and on those occaisions the sales ALWAYS include 30/06, 308, and only sometimes the other stuff.

I get the good stuff when it is available at decent prices and when I don't have time to reload.

I never said 243 and 7mm/08 were hard to find, I said the 308 would be easier to find, and often cheaper.

I have a 308 and 243 and so watch both flavors .... the 7mm/08 I peek at from time to time.

7-08 is becoming more popular as of late. Was just at Cabela's and they have more round choice for the 7-08 than I saw last year. It's fast, flat and a real easy shooter.

A .243 would be a perfect rifle for your/his needs. Like others have said it's a light recoiling rifle that will get the job done. Good luck!!