LibreOffice is exactly the same as OpenOffice.
However, OpenOffice became the property of the company Oracle when Oracle bought Sun Microsystems that oversaw the development of OpenOffice. Some people fear that Oracle might make changes that go against the philosophies of open source software.
LibreOffice was created by taking the exact same code as OpenOffice, and releasing it under a name that was not owned by Oracle.
So, to answer your question from the point of view of usage, there is no advantage or difference in terms of using the OpenOffice or LibreOffice... at least, not yet, as, so far as I know, Oracle has no significantly changed it. Ubuntu decided to use LibreOffice simply because the developers did not want to be connected to Oracle.