by schizoferret
I would say that Economic Liberty is the single best advance in the game, giving you essentially a fourth free action every turn, and you collect almost every turn anyway. Civil Liberties are also very nice to have, as the best source of mood tokens in the game. If you capture a large city, increasing it's mood is ridiculously costly - it turned out prohibitively so for me in my last game, making recapture of my lost largest city not really worth it.Autocracy is also good, with an optional fourth action (for 2 mood tokens) granted by Absolute Power and Forced Labor allowing you to actually have any use of captured angry cities.
In comparison, theocracy doesn't include anything that seems similarly useful.