BE GONE, BEAST
Vampires
My vote goes to making your character unutterably hideous, have the party know up-front what you are, and basically be the permanent "bad cop."
Wear extremely heavy, full-body concealing clothing wherever you go. Invest heavily into social skills and make it your job to get NPCs to reconsider negotiations with the actual party face if they've gone south. Be a master interrogator (who also probably eats the bad guy afterwards).
In combat do whatever you want, being a vampire doesn't necessarily have a niche there.
Anyway, I'd avoid hiding the fact that you're a vampire from the party at all costs. All that does is make it more annoying to be around you, and meta-game-wise, they're going to find out pretty quick anyway. At least if they know they can plan adventures at night and shit without you having to make excuses for staying inside or whatever.
>going into a session with a character concept that you don't have developed
Dude.
Why.
Go watch What we do in Shadows and Interview with the Vampire. At least you'll have something to work with as a concept beyond Dracula.
Otherwise, what system, any in-setting rules for vamps, etc. The more information you can give us the better.
>how did you become a vamp
>how long have you been a vamp
>who were you before you became a vamp
>what happened to the vamp who turned you
>how you do acquire blood
>what vamp mythos is present in the setting. Native soil, sleep in tombs, garlic, crosses, stakes, whatever. what is in play
And those are just the questions you need to answer off the top of my head.
>a smug piece of elemental evil on two legs
No, no, no, I don't like that
Dio is a fantastic antagonist but would make the most annoying, awful PC in the world.
>fantastic antagonist
Na
Ja
Alternatively, go full affable evil.
Do the right thing, all hero-like and stuff, as you would for any pretty cool guy.
You got their back. You pull your own weight and more. You are the perfect image of the average Chaotic Good adventurer, doing what's right when needed. They like you, they think that being undead is only a minor problem, since you really ARE like any of them heroes.
... and then you drink a local orphan dry.
"-What ? I was thirsty..."