This week's book giveaway is in the General Computing forum. We're giving away four copies of Arduino in Action and have Martin Evans, Joshua Noble, and Jordan Hochenbaum 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.