I refuse to answer this...it's like asking me what I like more "cake or icecream"...
No, just NO!
especially if I don't take CAS and BB into consideration...I can't choose...
for gameplay only, to me they are pretty equal, I guess it depends on how you play.
Spellcasters have more things to collect (like spells, potions, wands, brooms)
Vampires have perks that can actually change the way to play them/their personality, providing a way to make each vampire more unique
They both have sweet ways to mess with other sims :)