The HK91/G3 has a fatal flaw in a main battle rifle. It does not lock open on empty. In the heat of battle are you really going to be counting rounds? Murphy says the rifle is going to go "click" at the worst possible time.
The FAL is the way to go. Ergonomically it is the fastest of all when doing a reload. It reloads very similar to an AR15: as you're reaching for a fresh mag with the left hand, the right index finger is dropping the empty. Then you reload with the left and drop the bolt release with your left thumb. The guy with the HK91 is still fumbling with his mag, and still needs to rack the bolt, while you're back in action.
Someone mentioned the FAL forward grip gets hot. No need for that -- lose the metal handguards and buy the synthetic ones from DSA. It's $50 well spent and you'll never burn your hand again.
You can't ignore the economics of tons of FAL mags being available for $5-8, while HK mags are $25+, M14 mags are $50, and AR10 mags (when you can find them) are $75+. FAL spare parts are cheap and are everywhere.
None of these rifles are precision, 1-MOA, out to 1000 yards. Anyone who says that is full of it. If you want sniper accuracy, get a bolt gun with a 26" barrel. The intended mission of a .308 MBR is to hit 2-legged critters at 500 yards with iron sights and milsurp ammo. That means the rifle has to be capable of 4 MOA. All of these (FAL, HK91, M14, AR10) will do it. (Assuming of course that the shooter is a "rifleman".) In terms of reliability, I'd say all of the mentioned rifles is roughly equal. They are all made to operate under the worst of conditions, so a good example in any should be utterly reliable.
Buy a *good* FAL, not one of those $500 Century hack jobs. A decent FAL will cost around $1000 and up. But it's something you can trust your life on.