I had the NT and the screen was a little difficult to scroll on easily, and you could see the little mesh network underneath the glass. The HD is great to hold, although there's a hard plastic on the edge that might feel uncomfortable to the hand. I nearly bought one at Target, but I just couldn't get past the lack of good, inexpensive apps, and the one I used most, Scrabble, didn't have an HD version yet. I always had trouble navigating on the NT too, especially with files on an SD card, and the media and music apps were awful.
I went for the ipad mini, despite reservations about the lower resolution, but I was pleasantly surprised, even for reading. The greater screen area allows both 2-page landscape and portrait mode, and it rests nicely on my hand, sort of like the Kindle 3. Where it really shines, though, is as a gaming tablet--easy to hold and turn and tap, whereas the ipad is too big and the itouch/iphone too small for me. The web browsing is also much easier than on the smaller Nook Tablet screen, where I used to have difficulty hitting small links. I was also able to split my ipad apps and music and movie files between the two devices, to save some space and add variety.
But for those who just want a good tablet reading experience, with maybe some Netflix thrown in, the HD is a good choice. The Kobo Arc is also coming out this month, which has access to Google Play, so those looking for a good ereader tablet might want to wait and check that one out too.