The democracy is not only my preferred government, but it seems to be the best when used correctly.
You might be thinking "oh, but what if you go to war?" Turns out there's a clever way that some players use to fight wars as a democracy.
Basically you need to plan ahead and carefully allocate your military units. Build the majority of your military from a city with Shakespeare's Theater so there's no unhappiness, and bribe as many military units as you can from barbarians since they will have no upkeep costs and have them upgraded through Leonardo's Workshop.
When waging the war you need to control when the enemy tries to negotiate, and goad the enemy into repeatedly sneak attacking you so your Senate will interfere less. Your legislature will be less likely to accept peace with a power that wronged their constituents after all.
Another way to get around the Senate interfering is to have a friendly power to go war with your enemy. They'll ask you through diplomatic contact to declare war, and the Senate has no say in it.