I would think that a PDF format document would be the better choice if the goal is to have people print the flyer. The PDF format lends itself better to printing on printers with different resolutions so that it fills up the page. Since jpg is a raster format, the resolution is determined when the document is saved, and may print in different sizes depending on the printer.
Typically, the jpg file size will be larger than the PDF.
I think people are now pretty used to opening PDF files. While I wouldn't recommend them to replace HTML pages that are meant to be browsed, they are great for things that ultimately will be printed.
If the person that sent you the flyer doesn't have a PDF converter, I believe Adobe offers it over the web.