Pyra, and it isn't close.
Pyra will support you, love you and be there for you when you need help. I'm aware that most anons don't know this, but sex with someone you really, deeply love is way better than someone who you are simply attracted to.
Mythra will always be cagey, never wash the dishes even once and will keep her distance from you when you are sick. Don't fall for the "But she's hotter!" trick, anons.

Mythras are for memorable flings. Pyras are for the real deal.