It depends on what type of books format you use. DRM or no DRM and so on.
I have standardised on ePub and PDF if ePub isn't available. And use Calibre to convert anything else to ePub format.
There are a lot of really good apps for reading on Android.
I use Mantano Premium. But I don't use Calibre Companion. Instead I have a folder with all the books saved to disk on a wifi share, that I automatically sync to my tablet over wifi using the app FolderSync, when I add new books. I have tried CC, but I prefer using Mantano and FolderSync.
There is a free version of Mantano that you can test.