Brindleton Bay is my main world. It's big enough to have a lot of houses and community lots, so I won't need to visit other worlds to do things. It's also pretty and has the feel of a small town, without being too small, like Chestnut Ridge. It's simple enough where I can change its feel and identity by changing the lots; I usually make my Brindleton Bay an occult paradise. And I can play on most of the lots, because so many are located in good areas and have good sizes to them.
I like Chestnut Ridge, Moonwood Mill, Sulani, Copperdale, Mt. Komorebi, Glimmerbrook and Henford, but with those worlds, I only play on the same couple of lots because the world is so small, or most of their lots are small or in a bad place. So I'll usually play a single family (or two, in Mt. Komorebi's case) in those worlds.
Windenburg is where I dump old money European families; I like the world, but I never play in it because the community lots are pretty good, and I like to have my sims visit them. I used to play a magic school here, but then I moved it to Brindleton's big 64x64 lot, since the rest of my game revolved around that world.
StrangerVille and Tartosa would have been mainstays if they weren't so puny. Almost all the lots are small or isolated, and there are so few lot spaces that I can't put any new attractions. I just have one family here, and I only use them as background characters. But on the plus side, with Tartosa I can finally build some Mediterranean houses and not have them look out of place.
I usually use Del Sol as a dumping ground for celebrity NPC sims. Forgotten Hollow is a dumping ground for goths and vampires. Evergreen Harbor is small, so I'll only use it for rags to riches challenges, and the sims will usually move out once they no longer need to dumpster dive. I just I never play Magnolia Promenade, Britechester, San Sequoia, Oasis Springs, Tomarang, or Granite Falls.