In the TV series- Buffy actually died twice, and nearly died at least once more (in Seeing Red).

Okay so Phoenix it is for Buffy. Plus I find the whole - phoenix as a sign of Summer, and Buffy's sire name is Summers as being a bit poetic, as well.

Then the question goes to what would be best matchs for Kendra & Faith. For Kendra - I have Dragon or Tiger. And for Faith - Tiger or Serpent.

Note: of the current line - only Buffy & Faith will actually have a chance of becoming their respective aspects.