Here is the snippet to get the selected value for the item selected in a select one choice inside the value change listener

Integer in = (Integer)valueChangeEvent.getNewValue();

JUCtrlListBinding fc = (JUCtrlListBinding)ADFUtil.evaluateEL("#{row.bindings.SelectOneChoiceAttribute}");
String selectedValue = (String)fc.getListIterBinding().getRowAtRangeIndex(in).getAttribute("ListDisplayName");