You can just pick the one you like to most by the looks.
but if you care about how OP they are, Saffron is a good choice in my opinion
Also Cherry, Kerria and Dendrobium are good choices too depending on kind of team you want to build or which units you already have
But generally Saffron works great in any team really, specially for raid bosses but works great for everything.
She would be hard to replace in the long term.
I would buy her if she were in the daily deal.