Having a dog is essentially like having a child, except that child can't and will never be able to: talk, or do anything relevant/useful, or make any kind of meaningful contribution. But it still costs money, and requires attention and exercise on a daily basis. Oh and uses your floors as a toilet...and eats your stuff. Man's best friend indeed
Cats? They just chill, eat, go do *something* for like 8 hours, keep to themselves. No problem. Though they probably do also piss on your floor and wreck your stuff from time to time.
I'd personally have neither but if you made me choose then cat wins every day.