You just have the wrong variable names. The proper way to get any of these is shown below:
var client = Ti.Network.createHTTPClient({
onload : function(e) {
// Print anything you get back
Ti.API.info(this.responseData);
Ti.API.info(this.responseXML);
Ti.API.info(this.responseText);
// Parse your results
var results = JSON.parse(this.responseText);
Ti.API.info(results[0]); // Print first index of the array
}
});