I think that toads are among the least popular pets at Hogwarts, not because they are repulsive (they are beautiful) but ... really, who wouldn't want to have an owl or a cat as a pet? Me, I'd probably want a cat because I'd want it to stay in the house (dorm) with me. And I think this is also a thing of preferring a cat because there is a lot less 'work' to keeping a cat. Toads, you have to be very careful of! They need special place to live; certain kinds of food to eat (not just food off your plate) and so there is a lot of having to be very careful with them. Also, they are a prey animal for some, so you have to be careful around all the larger predators (cats, well, cats AND owls) because the toad could end up someone's meal. I think that the thing about 'not wanting to be caught' is a thing too. I think that most folks would prefer to have a pet someone who would at least want to be around you. But then again, different folks have different likes and requirements, so that's why the owl or cat or toad, I guess.