I've only seen the anime, and that was a good while back. This whole thing is making me wanna rewatch it and read the manga though. From my knowledge though I feel that Cassie would get along with Black✪Star and Soul the best. With the Thompson sisters she would get along with Patti and only slightly dislike Liz. She would take every opportunity to annoy Kid by bringing up his hair's lack of symmetry and messing with symmetry of things. Not sure of what her relationship with Maka and Tsubaki would be.

Note that this all comes from knowledge of the anime only. I plan on rewatching the anime and reading the manga soon.