Do not even think about Realm unless you are sure about what you are doing and how it works. Prefer to use SQLite instead.
Android Development: some of the best practices. Jun 2016 edition.
Stepan Goncharov
26621
if you try to make your app support app all the way to ginger bread than SQLite is a pain cause they changed the api many times but with REALM you can do it more effectively without even worrying about the Android version