DJVU is definitely the technically superior format compared to PDF, but support for it is VERY small, and a lot of the documentation is sparse and VERY arcane.
Every computer and nearly every device can read PDFs... DJVUs, not so much.
There is a lot of good information over at the DIY Book Scanner forums. Here is one topic I remember where they discussed methods on getting very small file sizes:
http://www.diybookscanner.org/forum/...php?f=3&t=2555
Or read a lot on the DJVU forums:
http://djvu.org/forum/