I wouldn't pick any rifle chambered for .308 for the top ten.
After the research on infantry tactics during WWII showed that GI's of the time would time and again wait for the enemy to close within 300 yards to engage and that only a select few of the draftees would actually engage the enemy. The idea of massed long range marksmanship with the infantry rifle, ie One Shot, One Kill, was taken from the forefront of military thought. The best possible weapon for an infantryman in this case would be an intermediate cartridge firing, full-auto capable rifle, to maximize the available firepower of the infantryman at reasonable ranges. It makes sense, if thought about on a practical level.
Given the choice, would you rather take potshots at your camoflaged, moving enemy at 600 yards with an ironsighted rifle, or conserve your ammunition until the chances of a hit were more likely?
The british developed a 270 caliber intermediate cartridge which was set to become the world standard, and the original FAL's were chambered in it.
However, the historically well documented backward stubbornness of the US ordnance department stepped in in favor of the full power cartridge marksman, and forced the .308 round down the throats of NATO. Thus, the FAL was never fielded in the chambering it was intended for. All of its fine qualities aside, as soon as the m14 saw combat against the kalashnikov, it was almost immediately proven out of date, due to poor controllability in full auto. The long range accuracy of the m14, while superb, never benefitted the US soldier in vietnam because the long distances weren't available, and even if they were, a reasonable draftee private wouldn't take 500+ yard shots.
The merits of .223/5.56 as an intermediate cartridge are somewhat questionable, but its full auto controllability and volume of fire provided by light ammunition weight are markedly superior to the m14/.308/7.62x51 system.
As far as criteria of judging service rifles, what is valid and objective?
Number of battles won? Number fielded? Length of time in regular service? Reliability? Number of enemy killed?
While we Americans do love our garands and 03's, it's a common misconception that we "won" the 2nd world war. The vast majority of the fighting took place between the germans and russians. If we rank rifles on any of the above criteria, the mosin nagant and Kar98k are surely the top two. One could argue that the kalashnikov rifles have won many battles and been fielded by many many armies. However, warfare in the second half of the 20th and in the 21st centuries has not been anywhere near the scale of battles like Kursk or Operation Bagration.