Depends on your personality! If you want a pet to just sort of be there but not too clingy, get a cat, since they're pretty antisocial. If you actually want "man's best friend" get a dog. A dog will actually want to be with you and to play and stuff. I prefer dogs. Dogs actually like the attention, but cats just do their own thing..
I think it mostly depends on your personal opinion plus where you live and your commitment to the pet. A dog needs room to play and exercise, and a cat doesn't need as much attention and room, I guess.
I'm a dog person. Both are a lot of work. Cats are less maintenance though, they clean themselves & you don't have to take them on walks. Dogs need to be bathed, & walked to keep a healthy weight. You have to clean out the litter box with cats, which is gross. Your choice!
Dogs. I know this is off topic, but.... do not get a monkey. They look and act all cute, but can snap at any second. Some people got their face ripped off, along with arms, legs, and other parts. Or all scratched up. You have no idea how dangerous they are.