A few thoughts:
FN FAL - has seen more combat than any other 7.62NATO rifle. Gas can be adjusted to work reliably with whatever ammo is available. Rugged, reliable, decent ergonomics and handling. Sights are not precision, but adequate for normal combat roles. Easy takedown and maintenance. Parts and mags are reasonable.
M14/M1A - excellent sights, decent ergonomics and handling. Prices are a bit high for rifles, parts, and good mags compared to other choices. Likes good quality NATO spec ammo. Can be finicky with other ammo. Get a non-wood stock so humidity changes don't affect POI.
G3/Cetme/HK91 - reliable and accurate. Adequate sights HK style is better than Cetme. Very reasonable parts and mags. Ergonomics and handling of a 2x4. Likes hard brass, soft brass tends to stick in the chamber. Very inexpensive parts and mags.
BM59 - a good alternative to the M1A. Rifles and parts are reasonable right now from Classic Arms. Mags are a bit pricey but VERY well made. Likes NATO spec ammo, but users report good results with heavier bullets too. Get one with the tri-compensator.
Nothing else has a decent combat history except the original 1960's AR10. Those are very pricey and spare parts are almost non-existent. FYI, a very nice Portuguese model just sold at auction for $9000!
Handle, and if possible, shoot, several to narrow down your choices. All of the above have worked well under combat conditions.