You know, a mindless undead loses its class levels when it becomes one, so you would most probably be stuck with a 1 or 2 HD minion (hardly threatening).
At higher levels, a Skeletal Hydra can really go a long way in terms of damage (especially with the Corspecrafter feat series). For now, an animal with Pounce and lots of natural attacks or a high strength should do fine. Generally, combat-wise, I find that zombies are much better. Although they only get a single standard action each round, their increased strength and hit dice make up for it in terms of survivability. Furthermore, a zombie gets a bonus to its natural armor too, whereas a skeleton's natural armor is set based on its size; that's something you want to watch out for.