As England, obviously, because you get a free unit (assuming on a new continent).
Otherwise, it all comes down to the balance - is the production you put into a settler, plus the lost population point from that city, worth less than what you'd get from a new city? It's always worth it if you can grab a new resource. I would suggest for any new city, you always budget for a settler and a builder. In that case, you should be able to chop/harvest 3 resources to get the first district free. In that case, then as long as the first district you lay down will pay off (ie. you want to place whichever district will get the best raw output, mostly based on which city-states you are allied with). You need probably at least 50 turns remaining in the game for it to actually pay off. I mean, even if you immediately chopped a campus in the city, you're still not getting a ton of science from that to make up for the cost of the settler/builder. Some things that can make it pay off better:
-If you have a lot of similar city-states, then the district that you place might be way more valuable. If you have 3 scientific city-states with 6 envoys each, then every campus will be giving you at least 12 science per turn.
-If you have a terrific location, then that might be worth it too. If you have a city that gives a +5 campus, then you don't need nearly as many city-states to make that worth your while.
-If the location gives you some sort of strategic edge, that can obviously pay off. I've settled on the edge of AI territory just so that I have some friendly land to upgrade my units before I start to attack them. Especially good if you want to plan an overseas invasion - you can float your old units across the water, and wait to upgrade when they're right on the doorstep of the AI.
-If the location has a lot of chopping opportunities (ie. forested land, or lots of stone), and you have the Goddess of the Harvest pantheon, the chopping alone might be worth it. I mean, 3 chops can give you 400-500 faith in the mid-game, which itself almost pays for the price of the builder+settler, not even counting what you get out of the campus.
-Obviously if settling the city gives you a needed resource, that's worth it.
But basically, if you're not going to chop in districts, they're not going to be worth it, because they'll take forever to develop naturally. But if you can chop in that first district fairly quickly, then they can definitely be of value. Although for me, most of the time by mid-game the only cities I settle are from captured AI settlers. In that case, just throw them anywhere because it's a free city.
