Rorona needs to die in a fire. She's horrible moe garbage so far as I'm concerned. Liked Totori, liked Meruru, but I might go with Ayesha as my favorite from that group. Also enjoyed the handful of older ones I played. Haven't touched Escha & Logy, and I do have Shallie, but haven't gotten to it yet.
Atelier is such a love/hate relationship for me. I love the idea, and I love a lot of things about the game, but I'm kind of getting tired of the totally budget production values, and I want more characters that are really made for female players, not just "my waifu" guys. I want heroines that I'd want to be, or can better relate to, but too often, the MCs in these games are airhead klutzes who have no business attempting alchemy. That's one reason I liked Ayesha, because she bucked that recent trend a little.
Edit: Oh yeah, one of my favorites was Atelier Annie. I loved how it eschewed combat for the most part in favor of just the collection and creation side of things.