Biggest pluses for Aura HD: higher resolution screen, physically larger screen, Kobo Sleepcover is nice and comfortable (if you buy one); the night-mode hack posted here works just fine to give a great in-bed/in-the-dark reading experience (see
https://www.mobileread.com/forums/sho...d.php?t=212162).
Biggest pluses for the Aura: lighter weight, you can change brightness by swiping up and down with two fingers; screen refresh essentially eliminated (you don't have to have the screen go to inverse video every few page turns); completely flat front (the bezel is flat with the screen).
BUT: the Aura Sleepcover is atrociously uncomfortable, in my opinion; there's no reliable night-mode hack for the Aura.
I have, and use, both, but find myself reaching for my Aura HD most of the time, rather than the Aura. But both are great ereaders.