I'd say dogs over cats. I love them both, I really do, but if I could choose between 1-2 (or even all 6) cats from my gf or my sister's dog, I'm def. going for the dog.
Going out for a walk with the dog is just great, that way I'm not walking him alone, but (s)he's also walking me! Having the dog jump and being excited when I get home from work, knowing we'll have a walk is just great.
I do however love the way a house looks or feels when you step in the room and see a cat lying on the couch, or how they keep your lap warm .
Hard choice but all in all, pretty much based on the character of my sis' dog cause she's so awesome, a dog rather then a cat :P.
And yes, a poll would've been nice