The best method for automating data loading in BigQuery depends on your specific use case and requirements. You should consider the type and number of data sources, the format and size of the data, and the frequency and latency of the data. If you are loading data from a supported source, such as Google Ads or Google Analytics, you can use the BigQuery Data Transfer Service for simplicity and convenience. If you are loading data from a custom or unsupported source, like a web API or an on-premises database, Cloud Functions or Cloud Dataflow can provide more flexibility and scalability. If you are loading data in an unsupported format, such as XML or Parquet, Cloud Dataflow is necessary to parse and transform the data before loading it to BigQuery. And if you are loading large amounts of data, Cloud Dataflow is also required to handle the volume and throughput of the data. For regular schedule loading, such as daily or weekly, you can use the BigQuery Data Transfer Service or Cloud Functions to set up cron jobs or triggers. However, if you need real-time or near real-time loading, such as streaming or event-based data, Cloud Dataflow or Cloud Functions can process and load the data as soon as it arrives.