This will be a short one.
There are many tools out there for creating, editing and comparing XML files but I wanted to mention this free and easy to use tool specifically.
Microsoft's XML Notepad is quite practical and handy for quick comparison of XML files. Although the codeplex page for the project has not been updated since Oct 19, 2007 and there has been no new development or release since 2007 (apparently) the tool is quite sufficient for most basic tasks.
You can download the tool here: http://www.microsoft.com/en-us/download/details.aspx?id=7973 (http://s.tl/bdD)
Here are the very simple steps to follow to compare 2 XML documents:
1) Run the application
2) Click “File->Open” and select the first XML file
3) Click “View-> Compare XML Files…” and select the second XML file, then click “OPEN”
4) XML Notepad will compare the files and display the results in a plain and clean way
Hope this helps someone.