I recently got my character to become both, I try to think of the vampirism as a consequence of lycanthropy since it seems that being a vampire has no benefits while being a werewolf has no downsides in this game.
Lets see...
100% resistant to disease
100% resistant to poison
100% resistant to frost
25% more powerful Illusion spells
25% better sneak
Night Vision
Notable Powers - once a dayReanimate a very strong dead body for 60 sec
Indivisibly for 180 sec
Bonus - Vampires are affected by the Restoration Perk Necromage, making them the most powerful mage in the game.
I'd say that's rather beneficial.