Political ones have failed, since with national currencies we end up with inflation and spending the resources of the future (i.e. debt).
The decision to "suspend temporarily the convertibility of the dollar into gold" has lasted indefinitely. This means the government can print its own money with no accountability, until it acquires everything and everyone.
Have you looked into proof of stake? It is a pretty good contender, but is vulnerable to Sybil attacks in case of a network partition. With no objective way to tell legitimacy (like "work" that was wasted in proof-of-work), a network partition can not be resolved.