Honestly I would say both but in case of limit break gacha, prioritize Miku ... Tsubasa could always appear no matter the gacha.
For her memoria, the more common is this one .
As for support unit, it's like I said, there none really for her, her stats make her a good addition, her main skill hit every opponents ... that's all.
Tsubasa, being a RED card and ... well Tsubasa, can easily be a really nice addition depending on your already made party.
Well I could've afforded both, but I did go for Miku since I already do have pretty strong Red Team thanks to have Maxed out Change the Future Chris, I was debating if the additions to Tsubasa's made her even have a place on the team comp.
As for their lowdowns ... well their main skill just make them go crazy for 3 turns and a drop of DEF for Maria, this aside their good .. too good to pass on ... and beautiful ... and so Beserk, I want Hibiki if not both.