I want them all (especially dragons), but Supervillains and (heroes) have the potential for versatility that other occults can't match. Give a sim red skin and fire powers and you have a demon. A ghost with invisibility powers could roleplay as a kid's imaginary friend. A sim with craggy rock armor and gardening powers could be the local earth spirit.
Plus, Supers could add random global events to the game, if you enabled them. (I imagine there would be a large fuss if there wasn't the option to disable random events.) You could go down to the bar one night and a brawl between heroes and alien invaders could be breaking out. A superhero might rescue you from a fire instead of a fire-fighter. Cross-pack events could happen too, like a villain could manipulate weather in the park, or a sim could communicate with animals telepathically and cause them all to chase someone that they don't like. With the new sentiment system, things could get really crazy.
