Democracy is the most flexible! Higher production, higher commerce = build units faster, buy them without losing population if you need to rush, more unit support with all that money, and more luxury to combat WW. Add Sufferage and Police, and you're good to go (if the war doesn't last centuries). War ends, and you can go back to your normal economy with superhigh cash flow and science development.
Seriously, what good is pop rushing? In a city of 12 ppl you can't even rush a tank cause it costs too much. But in democracy you can spend a few hundreds or thousands GP and get your tank, and your money replenishes on the next turn. No need to wait till your tank is only 3-4 turns away from completion before killing half your city's population to get it done faster, which in turn slows down future builds of that tank, reduces your overall income and science, increases unhappiness, etc.