^* 1) Mill/Bentham's fundamental axiom: the 'right' thing to do is the one that ensures the greatest happiness for the greatest number of people.
Family pet dying will only affect you and your immediate family. Person dying will affect their parents, children, aunts, uncles, grandchildren/parents, friends, co-workers, employers/ees, and more. These people's sadness may very likely have an adverse affect on their immediate and wider circle of acquaintances, and so on.
*2) Utilitarianism again: an average human will live longer than the average dog. Therefore the decision will have a positive outcome for longer. (although I don't want to open a new can of worms, surely most people agree that in a similar scenario they would save an unknown baby/child over an unknown adult)
*3) Possible future potential. A dog will never become prime minister/set up a charity/donate blood or organs/invent something that increase the quality of life for humans and/or animals/write a novel or create a work of art that influences millions/even become a doctor or firefighter that saves others in a similar hypothetical situation.
*4) Reason. Animals can of course feel pain, but they cannot rationalise/understand it in the same way humans can. If left in the fire, they would not feel the full spectrum of emotions (betrayal, terror, panic, loss, despair) that a child or adult would.^
Some very interesting points, silver, but probably too many variables apply for them to decide the issue at hand. For example, points 1 and 2 are referencing unknown quantities here - the stranger could be an ancient, nasty paedophile with no loved ones and whom any number would be glad to see the back of.
As for point 3, well my dog has actually given blood (for other dogs, obviously) - a thing which I, for medical reasons, am not in a position to do. Does that make him worthier than me? He's also participated in charity dog shows that have raised money for worthy causes and improves out quality of life by guarding our rather remote and isolated property that had a problem with marauders before his arrival.
Point 4 possibly hold some water, for some anyway, but for me I don't ned to quantify or justify his pain or fear. I don't want hi feeling any at all. In fact I would argue to the contrary that a conscious adult is in a better position to fend for himself, therefore the more helpless animal needs my assistance more. The unconscious adult would not be subject to those emotions, making the point redundant.