I agree, 7.62x39 for the reasons stated. Also (if you need more), it is a legal and decent deer hunting cartridge (nearly equal to a 30/30), unlike the .22s.
I don't think any of these rifles are designed for great long-range accuracy, so why go for a small caliber, high velocity cartridge? I could understand it if you were getting a full-auto AK (smaller caliber would probably be more controllable), but for a semi-auto, I'd stick with the 7.62x39 for the cheap ammo, cheap mags, and other advantages.
By the way, I took my own advice and bought two SAR-1s and a bunch of magazines (including 75-round drums - yet another reason to go with the 7.62) last year. I enjoy these rifles a lot.
Doug