While I love both, I find cats really hard to understand.
As someone who has raised many invertebrates, cats are far harder to interpret and understand than invertebrates.
I also find it harder to get attached to cats. If I pet them, I fear that they might suddenly turn on me without warning. Cats want to be left alone sometimes, and it's not always clear when and when not to give them their own space. While I like their independence, they're a little too independent for my liking. They understand but ignore your commands, which is infuriating and it's hard not to lose it. They can get in a temper with you and suddenly decide they hate you just because you won't let them sit on their favourite perch. Cats can be very demanding. I also like to look at my pets, but cats start to look awkward if I watch for too long. And as a person who frequently has unexpected changes, events, holidays, cats don't cope very well so then I have to deal with comforting them too, which can stress me out. And adding to that, it's almost impossible to go on holiday with a cat, so I have to hope that there's a trustworthy cattery nearby - at one cattery ours got sick, and there's not a huge selection or infinite spaces available.
Also, hunting. I hate cats hunting and the only way to stop them is to keep them in.
Dogs are not fault free either. I don't like overly friendly dogs because I find them pushy and they don't always check your body language and mood before running over to you (if I'm sad and wanting to be alone, I don't want to be knocked over by an excitable dog). Dogs are very playful and can be destructive. I also find them a little... disgusting, no offence to any dog owners out there, I don't like slobber and dog scent and muddy paws and the other things that come with owning a dog.
"Cats don't really care about you" is definitely not true. And "all dogs care about you" is not true either. Our cat will defend you at all costs if she realises anyone is in danger, and she'll follow us on walks even if she doesn't want to because she wants to be with us. She can seem apathetic to us at times, or only be interested in food, petting and having a lap to sit on. But she will show genuine affection and greet you excitedly. I've seen dogs who are either not interested in people or a one-person dog, you can't form a bond no matter how hard you try. I've heard of dogs who will attack people.
If I'm honest, if I had the choice between a cat or dog, I'd choose neither. I'd rather have a bird. Maybe I'll get chickens or doves one day.