I don't know...

First and foremost, I believe that favorites should prioritize all other units. If you like Ninian, then by all means go for her! Like Karla? Go for her, too! Legault? You know the response!

But, if you prefer to play more disciplined and logically, where you feel that all of your resources should be optimally spent to help you do well in Arena or some other aspect of the game--and not chasing after units that already have their role/niche filled by another one of your units--then you are better off passing for a future banner.

It really depends on how you want to enjoy the game.

I'd save my orbs for the upcoming banners.

I reccomend you trying to summon Bride Ninian. Maybe you prefer Karla, but, I would say a flyer-ranged dancer and will help in lot of situations. I have both Airzura and BNinian and they are the best dancers without a doubt.

Karla can be really fast and really good, but there are a lot of swords who can also work pretty nice or even better than Ayra/Mia/Karla hero prototypes. For example, Ike. For me he is superior to the girl, he can kill ranged units, tank enemies and kill them with QR and Divine Aether.

But there are not other units who can replace the flying dancers. I know what I say because I have actually all dancers, and they are very very superior basically for their mobility. The can be placed in all sites and that helps in lot of maps. Summon BNinian, she is also limited. When you get her, you will thanks me.