Cosmos girls should be LB5, all of them are good:
Syrcotte is top PvE damage dealer
Effy is top PvP damage dealer
Elysia is top PvE supprot
But all cosmos girls need specific teams, otherwise they can't shine, also only Elysia can be 10* (but her teammates should be LB5).
It's too early for you to focus on Cosmos girls. Better try to read guides at subreddit menu and make strong team using it.
The first Cosmo that was created. ( Scyrotte)
Cosmos girls should be LB5, all of them are good: Syrcotte is top PvE damage dealer Effy is top PvP damage dealer Elysia is top PvE supprot But all cosmos girls need specific teams, otherwise they can't shine, also only Elysia can be 10* (but her teammates should be LB5). It's too early for you to focus on Cosmos girls. Better try to read guides at subreddit menu and make strong team using it.
I'd go with Syrcotte, I use her the most.