Since the rifles will be about the same weight (9 lbs?), go FAL, because:
1. .308 has better ballistics, both external and terminal (with good bullets, of course). Standard .308 surplus is a 150gr SPBT at around 2700-2750 fps from a full 21" barrel. 7.62x39 is, I think, a 130gr at around 2400 fps. .308 reaches out to long-range better.
2. Sights on the FAL are better than the AK. All the AK's I've seen have a mauser-type rear sight mounted in front of the receiver. The FAL has a range-adjustable peep behind the receiver, more like an M14 or AR-15. This is subjective, but I prefer the peep-type.
3. FAL mags are $5 each, or $8 each for brand-new-in-cosmoline.
4. A "really good" scope mount exists for the FAL (DSA), if you choose to go that route. I am not sure a comparable quality mount exists for the AK.
5. The "Right Arm of the Free World", it has been used by over 90 countries [Jane's Inf. Weapons].
-z