One more Possibility:
<RadioButtonGroup id="RID" columns="3">
<buttons>
<RadioButton text="Domestic" id="Domestic" selected="true" select="onSelect_Radiobutton"/>
<RadioButton text="Commertial" id="Commertial" select="onSelect_Radiobutton"/>
<RadioButton text="Industrial" id="Industrial" select="onSelect_Radiobutton"/>
</buttons>
</RadioButtonGroup>
Controller:
onSelect_Radiobutton : function(evt) {
var _radioButtonID = evt.getParameter("id");
}