Currently, Xerxes have 4x AK multiplier, so she's strong atm. Downside of her is that her skill only works on Electric type enemy.
Jormungand is pretty. She's a bit stronger compared to Xerxes on normal terms(that is without multipliers) but her skill also activates conditionally which the enemy must be flame type.
Nostradamus. A pretty useful in almost every situation. Her skill reduces damage by 40% for 4 turns and can be used against any enemy. Even without multiplier, she's useful for her skill. The downside of her is that her skill activation is at 25%. 25% is pretty low.
In reality, whichever one currently has the x4 is the best possible choice. Either that, or choose whichever one you like the appearance of. If you're considering who to use Blin on, you should save it for event-limited sidians instead. While skills are useful, but since the stats of 4* units are quite low, so they still aren't of much help without a damage boost.