Indoor for city and partly outdoor for country cats.
City life is dangerous for kitties. Diseases are more fluent and accidents are more prone to happen. I would keep my kitty indoors in the city.
But in the country it is awesome for kitty to get out and climb trees, watch birds and just smelling the fresh country air does them so much good. Of course kitty cannot stay outside at night, there are fox and weasels and many other predators. Even owls.
So I would let them out a bit during the day in the country but not out at all in the city.