These are some of the reports collected by Google Analytics.

• Browser Report
• Visitor Acquisition Efficiency Analysis Report
• Customer Behavior Report
• Mobile Performance Report
• Site Diagnostics: Page Timing Report

Reports That Tell You How Your Content is Doing

• Hours & Days Report
• Referring Sites Report
• Content Efficiency Report
• Traffic Acquisition from Social Media Report

Reports for SEO

• SEO : Referring Pages Report
• SEO Insights for Google Organic (not provided) Report
• Keyword Analysis Report

By the way, all the reports given in the list here are important, but according to me, the list of reports given below is stored by Google Analytics.

1. Mobile Overview/Performance Report 
   
2. Traffic acquisition report
3. Channels Report
4. Navigation Summary
5. Landing Pages Report
6. Site Speed Overview Report
7. Goal Overview Report
8. Content efficiency report
9. Keyword analysis report
10. New vs Returning visitors
11. Bounce rate vs Exit rate report