My two cents worth...
A rifle, or any firearm, is simply a tool to accomplish a purpose. In this case it is usually to precisely deliver a piece of metal to a distant target. I happen to own a PTR-91. I had shot the G-3 at the Silver level with the German Army and felt it was accurate for me. The plus point is that the blinking thing is about as indestructible as you could wish for. A second plus is that it is recoil operated so you don't get as much gunk in the operating parts as with a direct-gas impingement (AR type) system or the dependency on the operating rod arrangement (M-14/FAL type). However, all weapons function better when clean so that may be a moot point for you. Drawbacks: no bolt hold open on last round fired; the iron sights aren't that great, but serviceable; ergonomics are interesting (the non-reciprocating charging handle is on the left side near the front sight and the magazine release is not a simple push button). However, the selector switch for safe to fire is possible the best positioned piece of hardware you could ask for. If you are a reloader, the PTR/HK family is hard on brass and this could be a big minus for you.

Of course the biggest single question after reliability is the rifle's ability to put bullets on target. Over open sights, any of the three (PTR, M1A, FAL) are superb in this regard. As with most things it will come down to personal preference and priorities. My priority was, for this rifle, robustness, so the PTR came home with me. There are lots of aftermarket accessories for all the rifles listed.

One tidbit you may wish to pay attention to is the caliber. These rifles are not truly .308 Winchester, but 7.62 NATO. The differences are small, but potentially important (headspacing being high on my list). Winchester manufactures 7.62 NATO cartridges and you can find bulk purchases of 7.62 NATO ammunition at various times from various dealers. The differences between .308 and 7.62 NATO are basically the specifications to which the cartridges are built. .308 can get pretty hot for a 7.62 rifle so I would recommend a bit of research before plunking down your cash.

Obviously I am a PTR partisan, but frankly any of the three are good, reliable rifles.