I like ScanTailor! I've used ocrmypdf for the OCR and compression steps. It uses lossless JBIG2 by default, at 2 or 3k per page; I'm curious how that compares to DJVU. (And my mistake, pdf and DJVU are competing container formats.)
If the PDF is from a scanned source, converting it to DJVU with equivalent DPI typically results to about half the file size (figures can vary depending on the specifics of the PDF source).
