> As a format FB2 is better than ePub because it separates the content from the view while ePub mixes them heavily.
Problem is that as soon as you need some typographical or layout feature beyond what is natively supported by FB2 you're out of luck.
With ePub you still have a chance of manually creating some custom effects before having to give up and fall back to a PDF.
Now granted, for your typical run-of-the-mill novel it's usually not a problem, because those rarely do anything non-standard with regards to layouting or typography.
However some books do play around with their layouting and/or typography, sometimes quite heavily. House of Leaves e.g. would be impossible to properly reproduce in FB2, and since that particular book goes really overboard in terms of playing around with the page layout, I think even as an ePub it'd be quite a feat to successfully pull it off.