I Love Harry. But in this scenario I imagine Lestat walking by Edward and ripping his head off for being an annoying brooder with nothing else making him interesting. Then he'd look at Harry and say sweet! and then he'd drink his blood.
Hmmm, that's an interesting scenario, But I don't consider Edward Cullen to be that good a fighter, his vampire savagery is about the only thing that keeps him going during a battle, whereas Harry Potter's courage, charisma and love for his friends will help him out even if his magic fails him.
Harry wouldn't kill Edward because he's lame like that and Edward would listen to some my chemical romance and light himself on fire because he's a stupid emo. So technically Potter would win by default because Edward would commit suicide.