Hands down, the Mauser. Mauser rifles were the rifle to field for the militaries of the world from 1871 well up to the early 1950s. The Mauser brothers had an excellent design acumen, and were able to refine the rifles and field an excellent weapon from the very start. Rather than trying to sell rifles and manufacture them all themselves, they would sell rifles made to specification, or complete tooled up factories complete with consulting engineers (thanks to the excellent business mind of Loewe).
Mosin-Nagant rifles are an excellent example of a peasant-proof rifle, sturdy, and rugged.