Some e-reader apps for ePub are Kobo, Nook, Bluefire Reader - off the top of my head. Generally, they can only read the books from their "parent" company because of DRM coding (i.e. Kobo can only read books from Kobo, the Nook app can only read books from Barnes & Noble, etc). So, if you buy an ePub book from a major company, then you'll have to use that company's app to read it.
However, if you don't have DRM protection on the ePub, the apps mentioned will read them just fine - and it won't matter which app you use. Then, it just turns into which apps presentation/menu system you like best.
Hope this helps.
Marilyn