To answer this, any Data Source is Best or easy to use subject to the requirement / need.

In my opinion any Connectors which are available in the Get Source Button, are best in its own way, it depends what do we need and from where?

Few Data Sources that I have worked on different Projects

1. SQL (Most Commonly Used)
2. APIs (very rarely used
3. JSON (Very Rarely Used)
4. SharePoint list (Most Commonly Used)
5. SharePoint Folder (Most Commonly Used)
6. Excel (for Learning and Training Purpose)
7. CSV (For Learning and Training Purpose)