I have both, and, yes, the Aura HD is nicer. And if you use Kobo's own Sleepcovers, the two units in the covers are almost exactly the same size, despite the bigger screen (because the Aura HD cover doesn't have the extra space on the top, bottom, and outside edge).
And if you want to get the Kobo Aura HD, get the Sleepcover from Chapters.ca (online, not in store) where it's half price ($25 instead of the usual $50:
http://www.chapters.indigo.ca/ereadi...ssories%3a1%3a