Probably vampire, for me. The werewolf transformation, if initiated amidst combat, it leaves you very vulnerable to multiple attacks as you are helpless to run or retaliate. However, vampire powers progress as you become the better stages. the werewolf powers allowing you to summon wolves, etc. require quests with Aela the Huntress (i think). People may hate you and all, and Lydia may dissaprove of the wrinkles. Yet vampires seem to be the better choice. Anyway, the disadvantage of no access to your armor, potions, spells, or weapons are not usable as a werewolf. Plus, you cannot be well-rested or have lover's comfort as a werewolf, with the exception of using the Lover's Stone (which I used for my werewolf, which helped). The bottom line is, you'll become more powerful faster and easier as a vampire than as a werewolf. In conclusion, the cons outweigh the pros for werewolves, in my opinion.
The Vampire imo is the same as the past Elder Scrolls Games...It sucks lol...I don't think drinking the blood of victims should weaken your abilities, I think that your abilities should grow over time, not how little blood you drink, doesn't make much sense to me...I think that you should have to drink blood to increase stats like health or magicka, but overall you gain your vampire abilities over time no matter what amount of blood you drink, I also kinda wish they put in different vampire clans like Morrowind...But anyways, I'd pick werewolf just because of how annoying vampire is...The point of werewolf transformation anyways is for nobody to know your identity and you can stay as a werewolf for almost your entire time playing because of the amount of foes you'd kill....So basically, you don't have to worry about your werewolf powers going away DURING combat, just be smart about using it. The point of the werewolf is to be FAST, hit and run attacks, not standing and fighting of course you'd die lol...However I think the werewolves power should increase over time too, as any mythical beast like vampires and werewolves, they either increase power over time, or if it is passed down bloodlines like a werewolves blood. I'm not entirely sure if what I wanted to say is all there but...I can't think of or remember the rest of what I was going to say.
Personally I think werewolf looks cooler, and is more manageable (being outside of form), but they just don't seem that great - too many disadvantages (but maybe I'm not playing them right). It just seems like they should be more, well - beastly...
I agree that some specific quests as well as more progression for both would be welcome (even in DLC form).
I say vampire is a lot better.
Vampires get a heavy burst to illusion at the cost of being very susceptible to fire damage and reduced stats during the day. It's also a hassle to have to feed in order to keep yourself from turning into the final stage (which will make all npc's attack you on sight). You also get many abilities which you can find on the skyrim wiki site.
Werewolves are kind of useless. Endgame, they don't deal much damage. Also, you don't gain any skill experience while in the werewolf transformation, meaning that your one-handed skill (or whatever damage-dealing skill u use) will not improve. I suggest the werewolf only in an unarmed pugilist playthrough.