If I was at Hogwarts and if I was a student there ... if I had my druthers, I'd have both an owl and a cat. I'm not very interested in having a toad as a pet!
Cats have a mystique about them which is rather awesome. They are not one to be trained into doing things ... yet I've seen some cats do remarkable things but it was because they wanted
to. Also, there is a certain level of intelligence that many cats have -- your 'cat' lesson points to that. There is a lot more in the way of upkeep for a cat, though, if compared to having an owl. One must make sure they have a place to stay and food to eat and litter boxes (even if the House-elves take care of that).
An owl, on the other hand, can and will take messages for you to almost anywhere. They have the ability to fly ... and soar ... and are regarded as creatures of great magic. They are practically maintenance free when you are at the school since they stay in their own tower, in a place specifically built for them and are fed by someone (the owl-keeper?).
I think, for funniest -- that would be totally on the personality of the cat or owl!
Alas, a student may have an owl OR a cat OR a toad. If I answer as a student, I'd say a cat -- and hope it is at least half kneazle!
If I answer as a Professor .... both. Although, practically speaking, I'd probably have a cat
Was about to post this and then realized it might be moot -- sort of like wands choosing their person, I think that a cat or an owl would choose me and that would be that.