EPUB is an industry standard and an open standard, while LRF is a proprietary format.
Compared to the other reflowable formats, EPUB is more advanced, supporting CSS stylesheets, SVG images, a real multi-level table of contents etc...
But the most important point is that EPUB will be used at an industrial level by the publishing industry and available across a large selection of devices.
Currently, it's still early days for the format, and the number of devices/reading systems that support EPUB are limited, but it'll change in the upcoming months.
Take a look at our EPUB help page on Feedbooks:
http://www.feedbooks.com/help/epub
Or at the official specs on the IDPF website:
http://idpf.org