My games are going so slowly that I don't really know that many worlds in the first place. While I have looked at quite a few worlds, I have only played in a handful, and that's mostly not because of any conscious decision. I have a game in Bridgeport, because that was the "default" of the starter pack I first got for the game. The game in Twinbrook got started when I bought Ambitions. I started something in Sunset Valley, because I wanted to see how the real Sims3 default world looks like. I restarted there because I thought about how you could improve it.
I just recently moved a few sims to a a custom world in order to spice things up. I'm increasingly looking at smaller worlds when I need a few sims made. Given my sims are breeding like rabbits, I will probably see a few more worlds in the future, as soon as I have to move them out of their cramped homeworlds.