I love them both. More broadly, I love animals. I prefer cats because they are a bit more self-reliant. As pets I really can't say because I've only ever had two cats and one dog (the rest rodents and fish) since I was little. I still have them both. One of the cats is pretty much the most loving and adorable little girl ever. She is minuscule and essentially my shadow. Cats are much cleaner (something very important to me) and teach themselves things. On the flipside, dogs are very loyal... I have a dog (that has awful separation anxiety >_>) that functions as a homing pigeon and, while he pours his love into everyone he meets and is quite playful, he is very, very loyal to my family. My cat is also pretty loyal though, so I'm lucky to have such lovely pets. The other cat is quite playful. All three are quite demanding!
Bigger dogs tend to frighten me a bit due to experiences I had as a small kid, but I really like small dogs. However, they are noisy as fuck and tend to yap, a noise I can't tolerate. Cats meow and purr, which are both noises I love to hear. ^_^
Dogs tend to... be hard to get to go away, or at least mine, who ALWAYS wants to be around people. Cats, at least in my experience, are quite intuitive, although the ball is pretty much in their court whether they go away or not. I am biased as hell because I REALLY love my cat more than any other animal (I play favourites...) for her incredible sensitivity to when I'm sick/injured/sad and her gentle spirit. Years before, I would've said that I prefer dogs, because I was scared of hissing and scratching cats, but most aren't predisposed to that. If you raise them like that, sure, they'll be like that, but I've only ever met gentle cats. Also, as mentioned, cats take care of themselves pretty well, so they're less... anxiety-causing. If my dog is ever not around I feel stressed because he's very much a home animal, but cats adapt well to outside and can hunt better.