I'm liking Bluefire so far; I prefer ADE's rendering engine to iBooks, if only for custom font support, but is more user-friendly than txtr.
So far, I've only got a couple of quibbles/suggestions:
1) I have to restart the app (double-tap Home, hold on the icon, close it, then reopen it from the Home screen) for a new book to show up in the library. Note that I'm only adding from iTunes, not from within the app.
2) My eye keeps looking for the page counter by the title at the top of the screen. It's probably a case of "it's not what I'm used to", but moving it - or having the option to - would be nice.
3) I'd like to see the option to force justification of text in books.
4) I'd like to see the option to adjust brightness more directly, without going to the settings screen; Stanza's up/down swipe for this works great.
5) Seeing progress through the book is good; I'd also like to be able to see how much I have left in the chapter, though. Either include "page 3 of 5 in the chapter" above the overall page count, or add page numbers to the TOC. Or both.