I've got the original KF and the KFHD 7". The KFHD is way better, to the point that I only have a couple apps still on the old KF (games I couldn't transfer & didn't want to start over).
I got the largest available storage space on the KFHD. I'd go for more storage before I'd go for larger screen size. To me (YMMV) the 7" size is perfect for hauling around, it fits in my purse

And I can get LOTS of games, vids, pictures, & books in the storage space.