Which army performed best after WW2?

[Redleg]

Conclusion : UN are great

Not at all - but that is a different topic.

Problems with UN missions are numerous. Politicial infighting between nations in the mission, poor communications, lack of common doctrine, lack of uniformity of equipment, and many many more. That some peacekeeping missions are a success is not because of the UN - but because of the will power of the soldiers of the nations performing the tasks.

[Marshal Murat]

I'd say military wise
Israel or USA

Israel has defeated numerous opponents, etc.

However the United States has gone against North Korea and China in the Korean War, and fought them to a stalemate. Vietnam is the same kinda thing. They have sucessfully defended or detered the USSR from attacking Europe, the United States itself, and I guess you could say the Middle East (Afghanistan).