I'm having a hard time deciding when to take over vs razing my enemy's city. Generally, I like the idea of stealing his city. But I played a very aggressive game this weekend where I went to war early on (I was on a 2 nation island- I wanted the damn island). I beat him easily, but the addition of his cities cut my income down to 60% on science, without me expanding myself (meaning there was a whole 1/3 of the island left unclaimed, and I was trying to take his 1/3). Whats the solution here- should I have razed his cities instead?

if theres forest around, and ur units are in danger, its probly better to raze the town and move into the forest for the nice bonus

I take cities that are near my border or otherwise valuable, and raze the rest. This way cities I take can use tiles that were already in my borders, and by razing the next layer of cities their borders can expand outward.