I've always preferred Sunset Valley, because that is what I know best, but recently I have been playing Appaloosa Plains, and I quite like that one. Everything is nice and close together, so your sim spends less time travelling. You can fit the film studio on the 60x60 lot and don't have to do too much town editing to make other things fit.
Hidden Springs is by far the prettiest. I like the town section of Bridgeport, but I don't like how it is so spread out, and the subways make travelling a lot slower.