def model_information(tileSource, format):
    """
    Return the model name or best information we have related to it.

    :param tileSource: a large_image tile source.
    :param format: the vendor or None if unknown.
    :returns: a string of model information or None.
    """
    metadata = tileSource.getInternalMetadata()
    for key in ('aperio.ScanScope ID', 'hamamatsu.Product'):
        if metadata.get('openslide', {}).get(key):
            return metadata['openslide'][key]
    for key in ('DICOM_MANUFACTURERS_MODEL_NAME', 'DICOM_DEVICE_SERIAL_NUMBER'):
        if metadata.get('xml', {}).get(key):
            return metadata['xml'][key]