FAL, easily. I've got 3 of them, and if kits were still easy to find and afoordable, and I had the spare cash, I'd have more. Probably a LOT more.
FAL is easier to build (no welding involved), easier to find parts for. I've not shot a G3 or CETME, but know a few people that have them, and they have complained about the recoil. One of my buddies has an HK 91 and he said that when he put the synthetic stock set he bought on it, it made the recoil way worse. Punishing. Plus the HK charging handle is way up front, not a consideration for some people but I wouldnt want to try operating the damn thing when in the prone, involved in a friendly Friday Night Firefight.
IF you want a battle rifle, the FAL is the way to go. If you want a target rifle, get an M1A. Either one beats the ever-loving dogshit out of the HK's, IMO.