They're all a little too bold and loud, though the Bembo is acceptable. I use Minion Pro Caption for most of my reading and find it superb at small sizes.
Slab serifs are OK for display uses, but not for body copy, unless you
want your text to be mechanical and shouty. There is no 'one size fits all' ideal font - the font used needs to reflect and enhance the content that it is presenting, and ePub's ability to contain custom fonts makes it ideal for that purpose. This has nothing to do with 'pretty fonts'.
You seem to be advocating that ebooks should be treated as typographically inferior to their paper counterparts, which is something I can't agree with. The limitations of current screen res need to be taken into account - I wouldn't advocate using a Didot or blackletter face - but there are a lot of options better than Caecilia.
Here's a comparison of Minion in Regular, Caption and Semi-bold weights. As you'll see, the weight increase in the Caption variant is quite subtle and enhances the distinctive features of each character while retaining the overall colour, while the semi-bold is noticeably fatter and louder.