If I include all life states, not just supernaturals... I really like plumbots a lot. They're low maintenance, they can change their personality as they want, and unless if they're evil, they're really sweet. Those with the "friendly functions" chip are totally adorable.
I also really like aliens, because they don't need beds to restore their brain power, and they have extra time at night to learn skills, have fun to reduce stress at work and do some house chores. And as they master logic (so they can teach their skills) and stay awake at night, I find that they make the best parents. Among all the sims I've played with, the aliens are my most well behaved sims, maybe because of this extra time to make them do useful things and to influence their free will positively ?
Fairies are my favourite supernatural sims. A lot of my sims are gardeners, so I find fairies quite useful. And they're funny. I really enjoy seeing them doing childish stuff. Too bad other adult life states can't do pranks.
Werewolves are funny too. I find their behaviour hilarious. I made a werewolf-fairy couple, the fairy loves pranking her husband, but she's a coward and she faints when she hears her husband howling ha ha ha !
Some life states I don't like as much...
I don't really like simbots. They're just too human, too organic, even their bodily functions. It's a bit weird.
I'm not a fan of imaginary friends, both because they're imposed on children (I've now installed a mod against that) and because children are unhealthily obsessed by them. That said, I still think my insane little girl has found a perfect companion in her imaginary friend. It fits her insanity well IMO. And they look cool once they're made real, I like their hair and eye colour, although they need plastic surgery to not all have a "face 0". But as I still can create an ordinary sim looking like this, other than for insane sims I don't really see the interest of imaginary friends.