In Drupal 8, we use the core Migrate API for
Upgrading Drupal 6 and Drupal 7 sites
Migrating sites from other systems to Drupal
Recurring imports from external systems (feeds)
It is a robust, flexible tool.
Drupal works best with structured data, and the Migrate API supports this: file attachments, related taxonomy terms, references to authors or other nodes, and so on. Along with the structured data, we also have to deal with blocks of text, and these blocks often contain HTML markup.