I think it honestly depends on what kind of play style you're interested in. I usually like going for a suburban family play style, so Willow Creek is the best choice for that (in my opinion). Also, it seems to be the only world you can actually experience every type of weather in... for me, it constantly rains/thunderstorms in Newcrest and Brindleton Bay (which can often get highly annoying). However, I mostly use Newcrest as a commercial district. I think I only currently have three houses there.
Oasis Springs is a desert... which is the kind of setting I never liked in games. Not even just in The Sims... lol Whenever I come across a desert in a video game, I usually ignore it (if possible) or rush through it as fast as I can (if it's required for the game's story). Also, Oasis Springs doesn't get snow... which is essential for my Christmas season gameplay. lol
Windenburg is too foreign for my kind of gameplay (I don't really care for the old English village theme). The same goes for Forgotten Hollow.
Del Sol Valley is too small for what it is... especially since it's supposed to be a Hollywood/Los Angeles kind of world... it should've been much bigger (like the size of Windenburg).
I don't necessarily have anything negative to say about San Myshuno. It's just not really my kind of gameplay. For me, apartments have only been used in The Sims to start out (if I choose to do so). I almost never make them into actual homes for my Sims to live and raise a family in.
I probably made this comment out to be much more than needed... lol Sorry if I kinda ranted for a bit. I'm extremely exhausted right now (been awake for almost 24 hours)... lol So I might not even know what I'm talking about right now... xD I guess I'll see later on when I actually get some sleep.