The Imperium of Man
New tank designs?? HERESY!
The German Empire after winning the First World War. Excellent education, stable, somewhat democratic and a strong economy. Would keep Europe from being swamped by millions of Arabs and Africans without turning it into a totalitarian hellhole.
The British Empire for it's Liberal traditions, wise leadership and impressive cultural output. The fact poverty has
increased in Africa since the British left is telling of the competence of their rule.
Republican and Mid-Empire Rome for it's stability (well excluding
certain Emperors) and highly impressive infrastructure (what was not surpassed until the nineteenth century) that allowed pan-European/African/Eastern trade to develop and create prosperity. Slavery, what held back technology advances in agriculture (perhaps the one area Rome was quite technologically weak in) appeared to be slowly dying out.
I'm tempted to say Yugoslavia, but it really was too dependent on Tito for survival. Tito-era Yugoslavia definitely though.