The last trial conducted of the Post-WW2 Western Battle Rifles was likely that of the South African Army in 1960. The winner was the FN FAL, followed closely by the Artillerie Intrichtingen (Armalite) AR10, then the HK G3 in third place. The M14 was apparently not included in the SA trial for any number of reasons, not the least of which were an international arms embargo and a prickly relationship with the USA. In any case, the FN FAL was considered the most reliable Battle Rifle at that time. Since then, the only real new developments have been in regards to the AR10. The further development undertaken by Knights Armament, the reborn Armalite Ltd, HK and others, have made the modern Direct-Impingement .308 AR pattern the most reliable (and accurate), semi-auto, military .308 in the world. This is evidenced by the US adoption of the Stoner SR25 and the more recent (2010) British acceptance of the LMT MWS as their Sharpshooter Rifle, the L129A1. The HK G28 (another .308 AR system) has more recently (2017) been adopted as the US Army's new Compact Semi-Automatic Sniper System (CSASS), the M110A1 rifle. There is no refuting the military dominance of the .308 AR within Western militaries as an intermediate-range sharpshooter/Designated Marksman Rifle (DMR).
The M14, in contrast, was pressed back into service as a stop-gap DMR only until sufficient SR25s could be fielded. Then it was passed on to the fledgling post-Saddam Iraqi Army... poor buggers. The accurized M14s, while capable of good accuracy and reliability, are very maintenance-heavy and in need of Armourer-level servicing on a much more frequent basis than the more modern, modular systems such as the Stoner rifle or LMT MWS.