I'm a little late, but it strikes me that it's a little early to talk about balance. I've read as many strategy threads as I can get my hands on and I can't help but feel that many people just haven't taken everything into consideration when they give advice.

Military Republic, for example: I've read several people claim that armies are generally useless and that "wars are decided in space", but personally I've found that taking over planets contributes more to the war goal than space warfare does. The longer the war drags on the more of a burden it is: the more opportunity there is to have an enemy fleet pop in and take out a mining platform, or make you lose some corvettes. Army damage helps those armies attack better, and also helps whenever you have armies placed to stop a rebellion. Army upkeep -20% also applies to all defensive armies as well, of which every planet has one, and as hinted at most players will probably have a sizeable invading army or two waiting about somewhere. A 15% discount on military stations is also better than you might think: middle to late game military stations (which is when I'm building them the most) can be a significant mineral investment, and 15% can add up to a pretty heft bonus.

I'm not saying it's the best government in the game, just that there's more to the game than people seem to be taking into account.