Outsiders often have better stats than one would expect for their HD, but Hydrae are definitely the coolest.
If using the Draconomicon rules, dragon corpses retain certain qualities, even when animated as skeletons and zombies, which could be a selling point. The Book of Vile Darknesses Corpse Creature and Bone Creature templates, used to create 'greater skeletons' via Create Undead, also work better than the standard Animate Dead versions.
Quite a few adventures make mention of necromancer-types modifying corpses, by using armor plates, or splicing weapons onto the ends of limbs, or selecting larger and stronger bones to 'strengthen' or 'toughen' the undead-to-be. Check with your DM if he'll allow the use of Skills like Craft: Weaponsmithing, Craft: Armorer, Craft: Leatherworking, Profession: Embalmer, etc. to stitch together superior skeletons. You might have to use three or four bodies to find the 'perfect' bones to do it, but if it results in a Skeleton with extra hit points (I stuffed him with padding, and laquered the bones so that they wouldn't dry out and become brittle), increased strength (I selected only the finest bones from work horses, so even though the Skeleton appears humanoid, it's made of much sturdier stuff, no, it's not a minotaur, that's an actual cow skull...), increased armor class (oh, I used all of the leftover bones I had to make a set of 'bone armor' to help protect the important parts) or more damaging attacks (I strapped six-inch iron razors to the edges of it's bony fingers!), it could be worth it.