Having owned all 3 major brands' ereader, (Nook Simple Touch, Kindle Keyboard & Kobo Mini), Nook still offers the best user experience, along with the ability to add an SD card makes it awesome. The back is also definitely nicer to grip. I also have a preference for page turns buttons, though the Nook's buttons are extremely hard to press (most reviews will mention this), it's still better than tapping the screen everytime you want to turn a page.
Currently only have the Kobo Mini, do go for it if you're one that likes portability & customization (it has many many many fonts, lazy to count!). In fact, it's shorter than my friend's Note 2, just wider. Syncing books is an absolute mess though, I had no idea what to do. Just used Calibre in the end (ebook management software). Have I mentioned that it's absolutely cute?!
Also, if you're one to get accessories with your gadgets, definitely get the Nook. B&N has truckloads of official covers.
Ultimately, it still depends on which models you're getting. Kobo Touch can add SD card, and the backlit models ain't bad either, though I've never owned one before. Final decision still up to you, can go YouTube to view the video reviews.
//note: a few days back, B&N was giving NookST with every Nook HD(+) purchase, dk if deal still going on, maybe you can grab one and sell the HD?
If you wanna molest my Kobo Mini before deciding which to buy, can drop me a PM
