Rep and Dem are, 9 out of 10 times, way better than the others because of the trade bonus. Undder either gov, when a tile produces at least one gold, it produces an additional gold. If you know how to utilize this (in other words, you road or rail all your tiles) you can make anywhere between an extra 6-21 gold per city. This easily covers unit support and other minor costs. In the inddustrial ages, once you have hospitals, 5 towns of... let's say 16 to keep it modest, already support 80 units, and most people have more than 5 towns just in their core alone.
Dem also has a 150% worker efficiency, however by then you probably aren't roading much. Still, can be useful for railing the frontier I guess.
In C3C, Rep has a free unit support as well, making it even more broken.
From what I hear, Mon is usually only better for AW (always war) games. However, it's really up to you an what feels right. But generally, the consensus is that Rep will get you through the
entire game.
If you look in your advisors report it actually costs more to maintain your cities and miltary
Your cities are probably a little unhappy after switching due to some WW or earlier whipping or something. I've noticed the population tends to be more irritable under Dem. Also, the reason why your military is costing more is that you no longer have any free unit support. In C3C I believe that Dem is the only gov to have 0-0-0 unit support since they overpowered Rep even more. I don't really see how Dem is supposed to be better than Rep anymore.
