#5: Hyena
I choose Hyena because he died as a hero after changing himself. Yes, he was a bad guy at first when he was working with Sniper. We would dislike him in the beginning. But as the story progressed in Ginga Nagareboshi Gin, he was in the process of changing himself from a dog filled with cowardice into a better and stronger dog. And during the battle against Akababuto, Hyena completely changed himself and became a really brave dog when he fought against cowardice to save Ben from Sniper. (For some reason, we don't see that whole scene until the flashback in Ginga Densetsu Weed.) Hyena saved Ben in the river and betrayed Sniper. Unfortunately, Hyena ended up getting killed by Sniper when they fought in the water. I say Hyena's death was really sad because of how he died as a hero. He was a dog that just changed himself from a coward to a brave hero. And he just died without having a chance of living longer with that great change. We could look at that and begin to like Hyena and then shed a tear when we see how he died right away. That's why Hyena's death is a little painful. Overall, Hyena died as a hero who terminated cowardice and found bravery in his heart.