I use SumatraPDF on linux with wine. If you just want a good reader nothing comes close, sadly.
> I use SumatraPDF on linux with wine.
I just discovered Foliate[0,1], which is a very small reader (252kb, deb) for .epub, .mobi, .azw, and .azw3 files. It's based Epub.js[2]. I was looking for a standalone epub reader (wanted to avoid the document management stuff) and stumbled across this gem.
It's performed very well on the epubs I've tossed at it.
[0] https://github.com/johnfactotum/foliate