My opinion? That is one sad and depressed dog!
Some basics are missed: Soft focus on the eyes in #'s 1&2, center composition in #3 doesn't really do much to the image for me, #4 is cute for you but I don't think the sepia tone really adds. I don't know but I think the B&W may look better, but just needs a tiny adjustment to the highlights (bringing them down) to make sure the image isn't overpowering.
#3 is my favorite just because she looks so silly with her tongue like that, as well as the droopy face combined. It just screams "I'm sad, but oh so funny."