This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
"Best" and "easiest" are always relative to the problem at hand, so we can't give general advice on that. The XmlFaq points to several introductions on how to use JAXP, the standard Java API for processing XML. You may also wish to investigate 3rd party APIs like XOM and JDOM.