Its got to be dogs. Dogs just form unconditional attachments easily in my opinion.
Not that i dont like cats, its just i like cats from afar. Honestly, i freak out if a cat jumps on my lap. Dogs on the other hand are always there, and dont really ask much of you, besides a walk, a bit of food. But most of all, what a dog wants, is affection.
My experiences with cats are generally, they come back when they want feeding (aka when no ones else will feed them). You hear about it all the time; cats going to other neighbors, simply because they get fed more. That shit wouldnt fly with a dog. Well, not as easily.