Directly from the publisher, the BBeB (LRX) versions typically look more like a printed book than the ePUB versions. But most of what I'm reading in this and other posts about ePUB dislikes is due to two reasons, both of which or easily solved:

(1) The publishers don't know how to format ePUB, much like some web sites look horrible and some look good, most ePUB publishers are terrible at formatting using ePUB. They need to learn what CSS is and how to use it, and Adobe needs to update their ePUB rendering engine to allow full utilization of CSS.

(2) The margins and sentence spacing issues are controllable. Currently you need to use a third-party application like Calibre to adjust margins after you have removed the DRM on an ePUB. However, there is no reason why reader firmware cannot allow the adjustment of margins, spacing, font, font-size, font-weight, etc. Most reader applications that have been around for PDAs, smartphones, etc. have these "look and feel" user adjustable options. Take a look at MobiPocket Reader, eReader, Microsoft Reader, etc. for PDAs.

Having said all this, I prefer the ePUB format. It is about half the file size of a bloated LRX file and loads much more quickly on slower readers. It is currently possible to remove the DRM then use Calibre or other options to adjust the look and feel of the eBook. And here is a major reason for me: I can edit the text of a ePUB with DRM removed. Normally that is not an issue. However, sometimes it is a good option.

Take The Iliad for example. For some stange reason many of the modern translations use the names of the Roman pantheon gods rather than the Greek pantheon gods. Homer was a bronze-age GREEK writer who lived way before Rome was a backwater village! I was able to rename the ePUB file from name-of-book.epub to name-of-book.zip, then extract the file to a folder. I then opened all the relevant HTML files in Dreamweaver and did a global search and replace on the dozen+ names of gods. Then I rezipped the folder into name-of-book.zip and changed its name back to name-of-book.epub. Now I have a more accurate translation. I am currently in the process of doing this to Genesis wherein I'm substituting the several names of god(s) from their generic meaningless English translations to their transliterated Hebrew forms. It makes for a much more accurate translations.

Note: These modifications are for me alone. Just as you can physically mark up a printed book you own, you can modify an eBook. You should not distribute it or share it though as that is not ethical or legal.

Bottomline is LRX is probably best for those who don't won't to make modifications or use the eBook on other readers. Whereas ePUB is better if you want to tinker with the eBook to better suit your needs.