It really depends on my mood and what storyline I've made up in my head for that particular sim. I tend to use different save files for different areas of interest or legacies, that way I can keep all the fantasy stuff out of it if I want to.
I love the vampires and aliens, but sometimes just old school sims are the most fun - but like I said, it really depends on what ive imagined for my sims.
Right now, I'm on a Cats & Dogs binge with no fantasy at all, even though I voted for Fantasy (because who doesn't wanna ignore realism for a while?).