No problem reading in either orientation.
See what your library recommends as their preferred reader(s)
For me to work with "NC Digital Library" I needed "Kindle Reader" for AMZ format and "Overdrive (for Android)" to read EPUB format.
The problem with readers is not their user interface, but their interaction with the library system (due dates, how many books out at a time, etc). Not clear how other readers will deal with this. Learning the interface took a while. Software was buggy (ie. how to deal with books lost in download?), and the library staff was not quite up to speed on all of this. They know somthing about Nook and Kindle, but not much about Android.