1) Yuisis. For a long time, she was just on the list of characters I wanted, but I didn't actively try to get her. Then the red version came out, I got lucky, and over time, I read about her, listened to her voice lines, and grew to like her ((c) Guy Revani Asahi). The Summer SR version is probably the last thing I'd want to get in GBF but don't have.
2) Vira. Her cat-like qualities are a minus, but I have too much history with her...
3) Olivia. If Vira was my first support character, then Olivia was my first spark and the reason I started playing in the first place. It would be fair to put her in first place, but I still have a bad feeling about all her seasonal lines, where she talks to herself and fantasizes about Pandemonium.
4) Helles.
5) Ferri.
6) Beatrice.
7) Magisa.
8) Monica.
9) Ilsa.
10) Dianta.
There are many other characters who could be in the top 10, because Dianta has a big problem in that she usually comes as a "set" with other characters, which I never liked.
There's also Shallem (there's something in her design that prevents me from putting her on this list with a clear conscience, but maybe if they make some kind of skin, it will be better) and Greya (but she comes with Anka, so that's a minus), and Rosamia, and Grey, and Rosetta, and Sophia, and basically many others.