Fascism is the best ideology and it's not even close

Fascism gives +3 production and +6 gold per specialist, which is insanely overpowered. It gets you the hammers you need to construct buildings, wonders, space race projects, and troops, and also the money to purchase things in towns.

In contrast, communism gives +3 science and +6 food per specialist. It is not as good because late game city growth does not depend much on the cities feeding themselves. Since towns can't have specialists, the +6 food per specialist doesn't really do a whole lot. +3 science is nice, but personally I don't find science to be a bottleneck in the modern age.

Democracy is possibly the worst of the three ideologies. It gives +3 culture and +4 happiness per specialist. +3 culture sounds nice, but it's arguably worse than the +3 science from communism mostly because culture victory is much less dependent on culture generation than science victory is dependent on science generation. Explorers are unlocked super early and the AI despite their doomstack explorer spam is too dumb to compete for artifact dig sites. The +4 happiness is completely useless because even without it it's already super easy to chain celebrations back to back.

Guess I'll just be an authoritarian fascist every time I play now :)