The Sims 4 doesn't have worlds at all, really. It has small neighborhoods that float in the ether, separated from everything. Yet, all of the neighborhoods manage to feel the same due to the same faces, everywhere. There is no genuine sense of being a "world" -- not for me, anyway.
I prefer having a single, large world that consists of several neighborhoods, as I have in TS3. I always choose the largest worlds that have an urban area, suburban, and rural, as well as beaches with diving lots and boat landings. There's room for every type of lot that I could ever need. As a result, with TS3, I never feel the kind of claustrophobia that I experience with TS4. If I get tired of the home world, there are three full-fledged vacation worlds to visit and to explore (with mods and custom worlds, the options are nearly endless). Each of those worlds has its own population so that I won't have to see all the same faces. Plus, as a bonus, collectibles spawn randomly so that each stroll through a world provides new discoveries. No two visits are ever alike.
I also enjoy that with open worlds, everyone keeps a schedule. When I'm not actively playing them, other household members still go to work, they still go to school, they go to bed. If I know another Sim's schedule, I can have my Sim meet them at their workplace to go for drinks, an early dinner, or a movie. It feels more authentic and more accessible than the constant teleportation and the sense that most of the world is forever-off-screen-and-out-of-reach that I get with TS4.
As far as I'm concerned, the devolution of the series back to single-lot play was not worth the tradeoffs. A closed world doesn't save time, it doesn't provide for better mechanics, gameplay, or fewer bugs. So, I'd pick an open world every time. Barring that, I'd choose open neighborhoods. I doubt that I would ever choose to play another single-lot Sims game.