.243 hands down for me. It just has so much more going for it. The 7.62x39 will work, but the .243 is better in my opinion.

And premium ammo for the 7.62 will cost just as much or more than the .243 and there will not be a lot of selection or availability in some cases. Pretty much everyone will have .243.

I am a big fan of finding a load that works in a gun and sticking with it. If he wants to plink get him a .22.

If you want a .30 cal see if you can get one in a 30-30, they are pretty simular but the 30-30 has slightly better ballistics and some heavier bullets I think.

I wouldn't rule out the 25-06 either.

Paul