I always try to stay under democracy, and at the worst, republic. This allows you to maintain your research, because of the bonus commerce of these governments. If I had a choice between monarchy or communism though, I would probably go with monarchy. This allows you to rush build temples with gold, instead of pop rushing under communism in a city that has probably been either pop rushed or drafted from by the AI. If you continue the trend, you will end up with a size 1 city that needs an entertainer for the rest of the game.