Working with XML: DomDocument or SimpleXML?

Hi, Just wondering what people's general opinion is on working with XML in PHP? I like working with SimpleXML but DomDocument seems more useful in some cases (e.g. working with XSLT transforms etc.). So what do you thing? Or do would you simply create a few utility classes to handle conversions? I have written a utility class myself that represents XML internall in either DomDocument, SimpleXML or String format and allows you to access it any of the three which means you can just pass XML "object" around and use it accordingly depending on the circumstances. I'd be interested to hear other peoples thoughts on the matter tho'. Cheers Col