Cats rule! They're elegant, pretty, clean, VERY affectionate when they happen to be in the mood, independent and arrogant. I wouldn't mind being a cat myself.
It all depends on the lifestyle you lead. I live in a 2 bedroom apartment, no room for a dog (it wouldn't be right.... they need a yard to run around in). My cats are great. They're independent, I can leave them alone for the weekend if I need to -- and they're pretty dog-like in their own ways (I've leash-trained both of my cats, they love going for walks)).