Provided your XML documents are of a reasonable size (think, < 1 megabyte, likely to fit into memory), using DOM is usually easiest.
So either use the DOM object, or SimpleXML, which is similar to DOM except it has a simpler PHP object structure rather than requiring W3C DOM methods.
Don't use regular expressions to parse XML
- They can't
- You won't be handling documents in different encodings correctly
- You will find that they match badly-formed documents, XML comments etc, where they should not.
Mark