Pretty much every crew has a repeating core for me. Collodi is the one with the most changes to that core, as he needs Puppets.
Primordial Magic - Cheap activation, card cycling, and potential surprise scheme marker
Nekima - Fast, smashy, and when used right can decimate a crew before she's taken down
Doppelganger - Cheat the initiative, copy abilities, interact while engaged. Yeah, just a massive pain for your opponent
Mr Graves - Tough, with a decent attack. Plus he can push models around which is massively helpful
Then there are some other models that make regular appearances.
Lilitu - Lure and a 4" melee give you some great board control
Johan - Tough, with a decent attack. Plus he has condition removal and Flurry.
Barbaros - Tough, and can push enemy models around. Nimble, which is very handy for certain schemes, or just charging people behind cover. Oh, and his Challenge aura is crazy good with Pandora
Terror Tots, Insidious Madness, Silurids - Great Scheme runners. They're fast, each with their own ways of getting up the board fast.
So yeah, there's a bunch of models, most of which you can buy by themselves as opposed to being in crew boxes.