This is a tough question. The type of question that requires in depth analysis into different situation. Let us begin:
I) Using a gun on a animal/human attacking you. In this case, i would use my gun on either in a second. If a towelheaded bomber is running at me, hes taking two to the skull and the same goes for a rabid bear. This situation is a draw.
A) Gun on animal/human for kicks. Now this situation is tougher. You see bambis mother, strolling with her kid deers telling them stories and BAM! She's down with a bullet through the brain. You run over with a big smile on your face and do high fives. Now, a man is with his kids on saturday at the park, whereing khaki pants with his shirt tucked in holding a video camera and BAM! sniped through the ear. In one side out the other. The kids cry and the single mothers run in fear. In this case, i would rather kill an animal. Less remorse.
1) Gun on animal/crackhead. A lazy animal bothers nobody. A crackhead on the other hand is exactly what his name says, a crackhead. In this case, i would shoot the crackhead before i shot any animal. The same goes for Rosie Odonnell in this category as well, she would die before a slug.
II) Bare hands, strangling animal/human. To strangle an animal, lets for instance say a puppy, you need to look that poor animal right in the eyes. They dont look in pain, but in sadness. Then you look at a person, for this example, lets choose jimmy fallon and his eyes look like hes surprised yet is trying not laugh but still is laughing. This feels good. Strangling jimmy fallon makes you feel so good that you would kill millions of jimmy fallon before you killed a single puppy.
III) Weapon such as hammer, knife on animal/human. To knock an animal in the head with a hammer is fucked up. Your most likely going to kill it and theres the chance of things getting messy. To stab an animal, i only ask why? Hitting a man in the head with a hammer is crazy. Your going to fuck him up but theres a chance he wont die. But you will severly fuck him up. To knife a person, is nothing, people get knifed all the time now its the new fad. So hitting a human in the head with a hammer and stabbing them is much easier to do then doing this to an animal.
A) Weapon such as hammer on dying animal/dying human. A dying animal wants to be put out of its misery. It was just ran over by an 18 wheeler along with 20 other cars on the highway and for some reason, god wont kill it. The only thing left is to die for this animal to end the pain. You walk up, say a prayer to god, even though hes the sick son a bitch keeping this critter alive, and you take it out of its misery. You feel bad but you know what you did was the right thing. Grandmas on life support and you walk in with a hammer and beat her in the head. Enough said. Killing dying animal with hammer, much easier.