I will back what
@Fishrrman says...
I use z-lib, though I use a free little joint called EBoox for an app... Does epub, for sure... It is simple and easy to use, though on a droid it must use GoogleDrive to sync - But it DOES sync, so I can go from my preferred tablet to my phone without losing my place - Which is my main requirement.
Would like to find an app that supports both PC and droid, and would rather it syncs with my normal critical data (which runs through MS OneDrive), But I am a noob at it, and have not found that much yet. This suffices for now.
Currently reading Clive Cussler, The Pharaoh's Secret.