Depends on your living situation. I prefer dogs but since I don't have a yard for a dog to romp in, I have a cat, actually 3 cats. Dogs are alot of work, cats are self-sufficient. Food and fresh water daily and a clean litter box keeps them happy. Whichever you choose, please adopt from your local shelter.
A puppy is better. Some puppies play more and appreciates you more as an owner, while on the other hand some cats/kittens sit like a couch potato all day long and never appreciates you. However, this depends on the cat's personality.
Cats are independent.(I love it.) Dogs always need someone to play with, I think. I had to walk my dog EVERYDAY :( He always looked down on the youngest of the family(=Me). (I admit that dogs are smart . . .)
Dogs are better than cats because dogs are playful for most of their life but cats are lazy for most of their life But both are good. If you have lots of time, a dog is fine but if you are busy a lot I suggest a cat.