The message of female empowerment and spirituality in Buffy the Vampire Slayer is diametrically opposite to the Twilight Series by Joyce Meyer. While Buffy and Bella both have love affairs with vampires the similarity ends there - Buffy never lets herself be dominated by Angel or Spike - on the contrary, she gives the orders.
Buffy falls in love with Angel and Spike in spite of her loathing for vampires, and hates it when those attractions upset her family and friends. And both vampires have to earn Buffy's trust and respect over time. On the other hand, Bella trusts the "sparkly" Edward and is ready to throw away all ties with her parents five minutes after meeting him. Won over by sex and expensive gifts from the Cullen Clan, Bella is besotted with romantic ideas of becoming a vampire herself - soul be damned!
Conversely, Buffy is willing to sacrifice Angel and Spike in order to save the world - choosing the greater good instead of selfish desire.
Besides all that, the writing in the Buffy series is so much more clever, irreverent, self-effacing and just plain entertaining. Twilight is a cloned romance novel that got lucky.
I could go on, but I'll let these pictures speak for themselves . . .