It seems that a cat would be a bad match for Hermione as a pet. Cats are playful and very disruptive, from my experience. NOT a good pet for a studious person with their head always in the books.
Of course Crookshanks was integral to the plot and ended up not being a simple cat, so she had to pick him. But it seems such an unlikely choice for her to make, compared to a toad or an owl.
Ron: "You bought that monster?" Hermione: "He's gorgeous, isn't he?"
(PoA). She chose him because he looked cute. Where'd the cool and logical Hermione go? :) – DVK-on-Ahch-To Sep 7 '12 at 4:53