In an attempt to answer the question "is there a best format" for recent ebooks from a mainstream publisher, I have made screenshots of Tolkein's The Hobbit from Harper Collins in six ebook formats on a Desktop PC. There are already a few screenshots and other comments on formatting in
Lord of the Rings Now Available! KINDLE, EPUB, PDF, LIT, and MOBI but that thread is too long to concentrate of formatting. Since all versions are presumably made from the same "master" copy, it isn't all that surprising that there is relatively little difference.
The six images are MOBI, LIT, eReader, ePub, LRX, and PDF. They are all from the 1st page of the 1st chapter. I can post other screenshots if anyone has other pages they would like to see. The readers have not been made consistent, for example I have not always chosen the same font or font size where this is under user control. I bought both a FictionWise and a BoB (OverDrive) MOBI, but these seem to be identical so only one is shown here. I assume the Kindle version is the same (it is the same filesize).
I was surprised that many of the illustrations are in landscape mode. This isn't too bad for a handheld device, but does not work well on a desktop.
The eReader and MOBI versions are about 1MB, the ePub, LIT and PDF versions are about 4MB and the LRX a bit larger still. This might imply that eReader and MOBI versions have smaller image files.
EDIT: FictionWise has released a "quick" fix of the eReader version. The final version is due May 1st. I have added its screenshot as a 7th image (original is image 3). This is more similar to the other versions.