I hadn't seen the SimpleObject variety so far, but I've used the underlying XML::LibXML wrapper quite a bit (in production, too). I am completely enamoured. It just works, it's very robust, easy on memory (much easier than any XML::Parser based modules), and lightning fast.

Plus, the libxml2 library it's based on has received lots of praise all around. It's known to often be the fastest choice; the accompanying libxslt2 is known as one of the most conformant XSLT processors.

I'd call libxml2 a pretty safe option to bet on.