My favorite world hands down is Sunset Valley. I don't know if its because I played this world first, but it is the most well done, IMO. And the layout works pretty well and its more easily adjustable.
I just recently got into Riverview though. I've played it before, but I'm just playing it again and realizing it has a great layout. I like "planned" communities, so to speak, so I like the way they grouped the school and gym near a cute neighborhood with a children's playground, and that there is a downtown area where I can add restaurants and shops, and a grittier town area too, plus the more rural areas with larger homes spread out.