That being said, the greatest improvement in the greatest number of people at the fastest rate is almost certainly a title held by the totalitarian government in China. Short-term but nevertheless evidence-based thinkers would struggle to see what the problem is with totalitarianism.
Also; reminder of my favourite thing-I-picked-up-from-a-bit-of-history, the other big advantage of democracies is they tend to be pretty reliable at winning wars. Voters are remarkably good at making armies work.