I personally don't like reading in iBooks solely because it has no night mode. Any other features were irrelevant to me since I don't like reading black text on white background on LCD devices.
I personally don't like reading in txtr because it has no night mode and the margins are handled in a manner that leads to too few words per page, and because the font sizes were not workable for me.
I personally found readMe on the iPad to be acceptable for fiction because it had night mode and I was able find font size settings that worked for me. It was not acceptable for technical books because bugs in the rendering engine did not render any further pages after images in some cases that I ran into consistently.
I personally find Stanza on the iPad with the update to be outstanding because:
- It has a night mode
- I am able to read text in technical books which have images successfully
- I am able to change the brightness of the font by sliding my finger up or down the page
- I can integrate with Calibre and O'Reilly books
- I can open books from Safari, or other applications.
I don't really care about whether programs have support for @font-face or not, since I usually prefer to change to whatever font is easiest to read, so that is irrelevant to me. I think it would be good if the renderer supported links, but that scenario has not come up yet for me.