Most of the free apps support epub.
Which app to use is a very personal choice. People choose apps for a lot of reasons varying from color schemes to option layout to syncing ability.
There have been several discussions on this forum about which reader is preferred. For example:
https://www.mobileread.com/forums/sho...d.php?t=190532
https://www.mobileread.com/forums/sho...d.php?t=188321
There are also many threads in the Android forum:
https://www.mobileread.com/forums/forumdisplay.php?f=225
FWIW: I started with fbreader and now use moon+ pro. I made the switch because moon+ supports position syncing between my devices. The free version did everything I needed, but I bought it to support the developer.