// try the most likely encoding
NSString xmlString = [[NSString alloc] initWithData:xmlData
                                           encoding:NSUTF8StringEncoding];

if (xmlString == nil) {
  // try the next likely encoding
  xmlString = [[NSString alloc] initWithData:xmlData
                                     encoding:NSWindowsCP1252StringEncoding];
}

if (xmlString == nil) {
  // etc...
}