In our school district we have been focusing on using ebooks with MackinVia. In the first year of implementation we looked at having all books with multi user license and with the capability to download for offline use. It is nice having one app with all of the books inside of it. Each student has a unique username and password. They get to add books to their "backpack" for ease of access and the books remember what page they were on when they left the app.
Personally, I use the OverDrive app with Great River Regional Library. I am big fan of all of the ebooks they have available to their patrons. I also like that they take suggestions for books I want to read that they do not have yet. The one downside to many of the books I want to read is the wait list. Just like in the physical library there have bought limited numbers of books. When they are all checked out you are put on a wait list and receive an email when it is ready for you.