Yes, that would get the best-looking ebook. The problems include:
- If you sometimes read at M in dim light or when your eyes are tired, you lose all that nice formatting,
- If you give it to someone else (presuming that's legal), and they prefer a larger or smaller font, it's not the best option for them,
- If you later wish to add content--images, annotations, whatever--it's a lot more hassle than adding them to an ePub file.
That said: I make PDFs to my preferences, make sure they're tagged (so I can reflow, even if I generally prefer not to), include bookmarks for a TOC, set the title & author as I'd like it listed in the Reader, link the TOC page to the doc pages (if I feel like going all-out), and then set the PDF to open to facing pages, bookmarks showing, show doc title instead of filename.
This allows someone else opening the file on their computer with Acrobat Reader to see a "book," opened as two facing pages, with the TOC off to the side.