Monte Vista has my favorite 64x64 residential lot-- it is on a hilltop next to a large, beautiful fishing/ruins spot. One of the prettiest lots I've ever played on! And I think the walled city in this world is great.
Rflong7/13'ds Legacy Island II is another favorite because the community center and the mall are both fantastic! And it has a perfect blend of types of buildings.
Dragon Valley is nice because of the strange, fantasy inspired people. The architecture is nice, too. And there is a beautiful lot with a lake and waterfall that I like to buy and have weddings at.
And Roaring Heights for the 30s atmosphere all the cute outfits the people have. When I'm in the mood to do a farm/country game, this is a great world for that. Everything looks like the great depression. And the boardwalk is fun.
Shalua's Cornucopia is also a nice, simple island world. I like using it for builds because it is nice and flat and has good lots.
I've recently been playing with Aurora Skies and find that to be surprisingly nice. And I also like Lunar Lakes as a place for Sims to start a legacy. Story-wise, I like to have an exiled alien (royalty maybe) start a game marooned as an immigrant on the Lunar Lakes colony, working toward the goal of moving to earth. The lots are really tiny on Lunar Lakes, so it feels like a good refugee camp setting. I think I may do a Lunar prison game sometime soon.