How soon do you switch to Monarchy ?

[The Economist]

I decide if I want a monarchy or a republic based on the situation, but usually a monarchy. Never ever ever switch gov'ts when you're in a golden age or if you're about to build a wonder!!

Also, don't go into a revolution unless you're sure that your military situation is okay, because you won't be getting any new units built for awhile, so sometimes you have to wait because of military reasons.

 

[USC]

Republic all the way, even in C3C. In fact, especially in C3C--since the "must-have" Philosophy is on the way to Republic and in fact, with a lucky start and a well-played game, I can get Republic as my free tech from Philosophy even on Emperor.

The extra unit costs are a small price to pay for
a) not diverting over to Monarchy from the "natural" republic path paved by Philosophy
b) not having an extra period of anarchy (since I will eventually want republic anyway)
c) all the various benefits that Republic brings over monarchy.

Nota bene: I play Huge maps most of the time, which I admit does skew things somewhat.