I prefer spellcasters because I like the idea of people who are made for magic. I like the spells, I like having my sims specialise in one of the magical branches. I am also very happy with the term spellcasters. My sims can be magical without needing to be called witches.
Vampires are very well done in sims 4. Objectively they are probably better balanced and developed. But I personally prefer magical being who are still alive, not undead and who don't need to feed off other sims.