I'm quoting you from this thread:
http://forums.civfanatics.com/showthread.php?t=203464
I assume you miss-posted there and wanted to post your question here here.
What's so great about Republic? I generally use Communism or Facism.
Once your initial expansion face is over and your core and semi-core is starting to develop, any government is better than despotism.
Communism and fascism are late game governments, if you switch from despotism straight to one of these two governments, then you spend the most important half of your game in the worst government type in the game. (I'm not counting anarchism of course..)
It is recommended that you switch away from despotism (your starting government) as soon as possible. And it is also recommended that you switch government as few times as possible during the course of the game.
So the choice is between republic, and monarchy. Communism and fascism, and even democracy make themself irrelevant simply because they come to late.
Monarchy:
free units support per city: 2/4/8 (town/city/metropolis)
upkeep cost per unit above the free support limit: 1 gold per turn
Military police limit: 3
Corruption: better than despotism, worse than republic.
Currency bonus: None
War wariness: no effect.
Republic:
free units support per city: 1/3/4
upkeep cost per unit above the free support limit: 2 gold per turn
Military police limit: 0
corruption: even better than monarchy.
Currency bonus: every tile producing at least one commerce produce 1 more
War wariness: unhappiness if you lose units, mayor unhappiness if you lose cities. But the government will remain stable, unlike democracy.
The currency bonus is such huge, it completely compensates the relative weaknesses of republic over monarchy. Basically, you get 2 times as much commerce.
You will have enough currency to spend on lux, to temporary compensate for any war wariness, easily pay the upkeep of 2 gpt of units above the free support limit, and then still have more commerce left to invest in science than in monarchy.
Provided of course, that you manage your empire efficiently, and that is often the main problem for players who are new to the game.