Originally Posted by Drip

Cactace was my first 6* as well, I got her from one of the first 6* ticket deals we had.

As for your candidates, I love the first 4, but don't have Serissa yet. Hollyhock isn't on any of my teams yet, but I'm thinking about having her replace Dipladenia sometime, when I get her skill a bit up, and maybe find her a dressbloom as well (other girls are ahead of her in the que for those things though)
Snowdrop and Acacia go very well with Epidendrum Swimsuit, in case you'd like to make a debuff squad sometime. Debuff squads have insane survivability, especially once you ampy (DEF and HP) and gear them up a bit.
Anemone isn't really good on her own, but works well in a counter-squad. And her special just looks awesome with those lighting flashes.

For the silly team, I'd suggest either of the Violas, by the way.

The Violas are a bit too loli for me, and while I've pushed the boundaries a bit for a couple designs I really like (Pumpkin comes to mind) I think Viola looks even younger and is a bit off-limits unless I pull her randomly via Gacha.

I ended up choosing Snowdrop, her ability with the attack reduction for enemies seemed useful and I do like her appearance. Hollyhock, Acacia and Serissa will all join the squad eventually. Also hoping for some 5-star ticket offers so I can nab a couple other characters I want to flesh out my teams, like Iris, Ardisia Bride, Cactace Bride and Sarcandra.

Eventually, I may put Snowdrop with Epidendrum Swimsuit on the silly team, but for now I'll groom her to join the front lines with Victoria Bride / Madonna / Ardisia / Cactace.

It's too bad nearly half the character designs for this game -- particularly with a lot of 6-stars -- seem based on way-too-young-to-be-legal loli archetypes. Maybe it's just even more popular than I'd guess as a preference in Japan.