Series Saga

Whats the difference between saga and series?

And what is the correct one for Twilght?

It’s exactly the same. Apparently Saga is a more fancy term and it’s a clever marketing tool. It’s not a matter of which one is correct or not. You could use either one and you’d be right even though Meyer refers to it as the Twilight Saga.

DBAX FoP Series: Universal Chaos Saga pt 2: Legendary Super Saiyans