I'm using
Pocketbook. It has all the basic functions that I need (except for an intuitive bookmarking system. I used to use
Moon+ Pro but it's epub rendering is sometimes horrendous I cringe whenever I'm looking at it.
I'm still trying to find a better one.
Mantano seems promising but I've been seeing mixed reviews on playstore and here. But
Pocketbook works really well for me right now.