Umm, I can't make up my mind.
Argument for Unicorns: To eat a whole dragon, only because the idea of eating a unicorn seems cruel.
Argument for Dragons: To eat a whole unicorn, cause dragons are epic and already have a bad rap in most movies and books. And if not they are used as steeds who aren't independent or emotionally capable enough to live without their rider when said rider dies. (Eg. Pern Dragons go In Between upon the instant their rider dies and blink out of existence. And not to mention the whole dragon egg entrusting and several other plot points/reasons in the Inheritance.
Conclusion. To eat a whole unicorn.
Dwarves or Elves?