I indeed have expertise on that, and that expertise says:
don't bother! 
It's sad but true. My daily reading is split roughly evenly between Marvin and GoodReader, precisely because converting PDFs to EPUBs is often a hopeless undertaking. And, many books (especially old, scanned editions) are only available as PDF files -- or the EPUB versions of the same texts are of such ridiculously bad quality, they are unreadable. (Yes, I'm talking about you, archive.org.)
Only this weekend, I was converting a short novel (novelette), 25 thousand words, 45 pages of PDF source file, from PDF to EPUB, precisely so that I could enjoy reading it in Marvin, rather than GoodReader.
I used the best available OCR software for the conversion, which is FineReader.
Even so, it took me nearly 5 hours (!) to convert the PDF file so that I was satisfied with the EPUB result. It's just
impractical. However, this was a novelette I deeply cared about, so I was willing to sacrifice the 5 hours of my time for the conversion. I would, of course,
not be ready to do that on a regular basis, because my remuneration for the work was exactly 0 cents. The only reward I'll get will be the pleasure of reading that file in Marvin. Hell, that's enough for me (in
this special case).
