Moon+ in portrait mode on Nexus 7 is great. No complaints there.
(Looking forward to Android 4.4 which will make it possible to hide the 3 Android buttons in Moon+, extending the screen real estate; this now only works when flipping pages with the volume button.)
But for things other than e-books, like browsing webpages or reading PDF files, the iPad's aspect ratio of 3:4 really strikes me as more suitable.