I know it says admiral, but I'm going to include some commodores, since that is equivalent to rear admiral, lower half.
Commodore Robert Wesley. A good, competent starship commander. Great to see another good officer who isn't on the Enterprise.
Commodore Stone. Also competent. He had to do an unpleasant duty, and was a professional about it.
Commodore Stocker. Even though he was completely out of his command element and therefore completely incompetent, he was basically a good guy. He didn't even want to take command for command sake, and (as I recall) first tried to get Spock to assume command. Not power hungry, but just trying to do what he felt was best for the ship and her crew, including the ailing officers.