XSLT & XQuery :------
xslt is mostly used in the soa suite (jdeveloper also supports the graphical mappping of xslts) and the osb is more optimized for using xquery and eclipse has a graphical mapper for this one
xquery can also be used in jdeveloper/soasuite too but you will need to create the xqueries by hand and use the function ora:processXQuery to make use of them.
besides that both 'languages' will suite better for certain logic which you try to execute (template matching, recursive calls etc)
