I'll admit, well timed question since I'm a novelist that's published a novel with vampires in it (and other creatures, don't worry, only one person in the whole thing sparkles and he's marked for death) and I was wondering the same sort of thing not long ago.
Truth be told, while if I had to choose one or the other I think I miiiiight lean towards the timeless classic... I think any good author could have crapped out Twilight after enough liquor (Meyer herself wrote the damn thing in 3 months and got it published in 6). So I think I'd write the timeless classic...get a pseudonym and write out the crappy money maker under that alias (much like Stephen King has done, repeatedly).
If I absolutely had to choose though, a little money now means I get to keep writing. A lot of money later means no one in my direct family has to worry about their kids going to college for several generations. I'll be dead someday, but they'll have foundations and awards with my name on it that will make sure that people like Stephanie Meyer never become the dominant power in the thing I love.
So, I'd like to write Dracula, it'd do more good for humanity, my family and the world in general than a piece of crap that makes me rich and famous for a decade before people forget who the hell I am (no one's going to remember Meyer after this, her follow up book series "The Host" has barely blipped on anyone's radar).
In the meantime, I guess I'm going to find out which I get. Shards of Glass by Jeremy Varner, available on most major online retailers and the iBooks store for only $2.99! Yeah, I know I said I want to write the timeless classic... but as a friend of mine once said, "he would like to eat something other than ramen".
Truer words never spoken.