1) FAL - "Right arm of the free world" an excellent rifle and pretty upgradeable, fairly to very accurate. Parts and mags are reasonable and easy to find. I like shooting mine, but would not want to carry it all day, it's pretty heavy.
2) M1A's, etc. - no experience with them, can't help you there. I have always wanted a Poly M14, but most are over $1000 now.
3) CETME/PTR - I had a cast stainless CETME(one of the good ones, better than stamped steel), shot fine. I got rid of it because of the fluted chamber that tends to mar the brass a bit and is not conducive to reloading. Very inexpensive mags($3-5 each). Somewhat upgradeable.
4) AR10 - You didn't mention these, but thought I would bring them up. I don't have one, but some like them if they also own an AR15 for the fact of identical controls, some parts interchangeability between the two. Mags are getting cheaper lately.
5) Saiga .308 - Another choice. I just sold mine. If you like AK's, this can be converted to pistol-grip style. Mags are pretty expensive($35 and up, each) and not as readily available.