Civsassin
Immortal
In a game like CiV, absolute statements of advantage or disadvantage for a particular course of action are never correct. One may be better than another for a particular play style; howeer, whether to annex, raze, puppet, or return the conquered city is a decision that each player has to make based on his/her goals for the game. Each has its place. If you are intent on war mongering, razing as you go gives you just enough time to heal your units in friendly territory and move on before the razing process completes. If you are having happiness issues, razing or puppeting may be better than annexing. If you are striving for a cultural victory, the same applies. However, if you need a few city's in which you to control production for the sake of building units or something else, annexing may be the way to go. The decision is usually based on the situation or play style. I prefer not to commit to a particular play style to adjust my game based on the random situation I find myself in each game and what I need at the time.