A good city postion is one that has access to at least 1, even better if 2, food resources, the only exceptions to this is if you need iron, or bronze or oil or some other type of highly useful resource an the only way to get it is to found a city in a poor location, things like fur etc just wait until your borders expand over them, it's not a resource thats worth the maintenacne costs of a unproductive city to have