5 star upgrade

That is a very tough choice. The question to ask then is what does your team need most? The fastest and strongest Axe wielder who will die to a sneeze, the pegasus rider who will be able to take on armors and cavalry, but will almost completely rely upon flier specific buffs, or the ultimate mage counter who can perform no other role reliably?

They all have pros and cons, but it's hard to answer which one is best without knowing what you actually need.

Raven.
I personally prefer Caeda with Atk boon & Felicia with Spd boon.
Caeda got 4 atk for boon & she's fast enough with neutral speed.
Spd boon Felicia to prevent her doubled by blade mage.