I am a werewolf because the game won't let me become un-werewolf. (kinda spoilers ahead, if it needs to be said).
I did the quest/event in which you toss the head into the fire and fight your ghost wolf. It rid me of my ability to turn into beat form. Despite this, however, my stats screen shows my days spent as a werewolf increasing. As well, I am unable to become "well-rested" while sleeping in an owned bed, although I do not get a message anymore that my beast blood kept me from getting a good night's sleep.
So I'm just going to finish up the game's story and spend my future characters doing some of the institutions I missed out on, like the Bard/Magic Colleges and the Brotherhood. Though this glitch(?) hasn't stopped me from putting 90-100 hours into it so far.
EDIT: I'd like to be neither, found that neither side presented any points worthwhile. I don't like being a werewolf for in-game story/lore related reasons, and being a vampire has more weaknesses than strengths for me to want to keep it up.