Doesn't matter really, as both can be worked into a mage's background. I don't care for either forms myself, but if I had to pick one, I'd say werewolf. The vampire lord model looks terrible, but that's just me, but as always, there are mods which can address that. Neither form offered enough utility for me to bother giving up using my own weapons/powers. I saw them as purely an rp thing depending on which you wanted to be.
OP-If you are on PC then become a http://www.nexusmods.com/skyrim/mods/40607/?!
None of the Vampires innate powers would work on a Werewolf, thanks to Beast Blood. Vampires can teleport, but Werewolves can close the gap pretty well. Werewolves are completely melee types, and those need to be in your face to do anything - Vampires have the advantage here since they are prone to be spell casters, especially in Vampire Lord form. That being said, going by what we know the two are capable of doing in the game, Vampire would win owing to being a ranged fighter. If a Werewolf corners a Vampire, a quick death will commence, of course.
-From a Werewolf user.
Edit: I did say they can close the gap pretty well, but this is assuming their frontward dash attack will fire off. Sometimes it bugs and wont fire on the first button press.
It depends on your play style. I dislike magic so vampire lord does not appeal to me in the least. Plus the blatant copy of Underworld for the vampire lord is disappointing. AND the transformation makes no sense. Its one thing to suspend reality for a moment as your armor is replaced by fur as a werewolf. But explain how turning from a human wearing one set of armor, into a different form wearing another set of armor?
People will argue the benefits of each form all day long but in the end it comes down to your play style and your character.
Give me werewolf form though any day and I'll wipe the floor with vampires and vampire lords.
If you are on PC I would try that Lich mod, it looks cool. But as a pure mage I personally prefer to be a werewolf because they are stronger, in my opinion, than the vampire lord when it comes to damage output and with the werewolf tree completely maxed out you are pretty unstoppable. I also think it adds a whole new fight style to your mage, in human form you are strong with magic and what not, but you also have your werewolf form which adds melee damage to your arsenal.
You get a bunch of buffs,and get a super powerful transformation to go with it.
C'mon guys, I linked to the Undeath Lich mod in my first post!
vampire, the master of illusion or whatever its called that makes vampires illusion spells work better is definitely more useful for mages.
Neither are really that great. I mean, the only thing about the Werewolf that is cool is the disease immunity. And Vampire is pretty much cons that come with stuff that you could probably copy most of.