JSON is the preferred format if you're looking to access the most detailed data, ideal for app developers or more technical integrations.
CSV allows you to quickly import your data into Excel or a database. CSV format flattens all sub-collections, returning only the first value for a sub-collection.
RSS format allows you to integrate your worker's scraped data as a feed into another program that reads RSS.
HTML format is intended for use with Excel Web Queries, allowing Excel to dynamically load content into a spreadsheet by parsing an HTML table.