I don't know why, but I find no similarities in Twilight and VK at all. I mean, Bella and Yuki's personalities are totally opposite, Edward does not resemble Zero or Kaname, and the 90% of the vampires in VK academy find Yuki annoying(which she is so not) rather than dote on her like in twilight. Does people only say that because it's both vampire stories? I don't understand...
There are some similarities between Twilight and VK, the really small things that makes each storyline unique.
1. Vampires are always so beautiful
2. How both 'types' of Vampires challenges traditional conventions
3. How there is a human (well assumed anyway) girl that falls in love/admires a inhumanely beautiful vampire.
4. That both female protagonists love the 'enemy', eg. Yuuki also cares deeply for Zero, who utterly despises Kaname, and vice versa with Bella and Jacob.
5. Not all the vampies in Twilight, dote on Bella - Rosalie, for instance.
These are a few of the small things that i notice .