If you're into family play I would recommend Parenthood. It adds a lot of new gameplay for that, plus some really nice CAS and BB stuff. If that's not your thing, I would go with Seasons or Cats and Dogs. Seasons is great because it changes how the whole game looks, plus the holidays are really fun (although they do get repetitive after awhile). I also really love Cats and Dogs, I love giving my sims pets and the realism it adds to the game, plus Brindleton Bay is a beautiful world. Also, both Seasons and Cats and Dogs have really great CAS and BB stuff, too.