In my opinion, the very best 7.62X51 calibre fighting/sniping rifle is the Knight's Armament Co, SR-25. It was a favorite of the celebrated sniper Chris Kyle.
There is so much wrong with this statement I don't know where to start, but I'll give it a shot.
1. Chris Kyle was in the Army, he didn't have the luxury of choosing a rifle. He used what they gave him.
2. The Army does not buy the best. They buy from the lowest bidder that meets their specs.
3. The SR-25 is still a gas impingement (GI) not piston impingement rifle.
4. Piston impingement are a major improvement on gas because they vent the carbon and heat outside not right back in the bolt. That translates to superior reliability and longer sustained rapid fire in battle. As some put it " GI guns poop where they eat".
5. A guy at my range has a KA SR-25, has the same 20" barrel length as my POF and is not nearly as accurate as my POF we have tested it. Not only that he paid almost twice what I paid.
6. Additionally the SR-25 is not NP-3 coated. NP-3 is a special electroless nickel-based finish for stainless steel that deposits sub-micron particles of Teflon in the pores of the metal thereby making self cleaning/lubricating.
7. If you drop an SR-25 in a puddle, your done. The water in the gas tube will cause the rifle to explode the next time it is fired, if not cleaned.
It is unlikely that the military will ever buy a rifle like a POF or scope like a Swarovski. Their standards are way too low. Maybe some special forces units, but not the whole military.
Please don't use the military as a benchmark for quality. Those of us that have been there know way better. For god sake they are still using the .223 which was intended for jungle fighting (low visibility, close quarter engagements). We haven't had a jungle war since Vietnam. As usual they are properly equipped for the wrong war. In a desert war like Iraq/Afganistan the extra range and penetration would save lives.
When my son-in-law was in Iraq they quickly discovered that they were at a disadvantage because when on patrol the enemy would pop up from behind mud walls. The .223 couldn't penetrate the walls but the Ak's 7.62x39 did, so they had to retreat behind corners. That's why the Army started taking M-14's (Korean war relics) and issuing two per squad.