Cats all the way. I've had both, cats are more intelligent, and more independant.
Currently I have two cats, Bonnie and Clyde. Bonnie is the archetypical supervillain cat. She is lazy until such time as she needs to do something. Like body slam a bird, or beat the crap out of Clyde cause he's being a jerk. I usually sit in my spinny chair with Bonnie on my lap. Mwahaha :3
Clyde on the other hand is extremely hyper. All the time. But he's not stupid, if he wants attention, he knows exactly how to get it. Taking things off the fridge, finding my keys, sitting on my keyboard, playing ninja on the window....
But yeah, you can't really engage in a battle of wits with a dog. Cats on the other hand are quite clever. Lots of fun