In your experience which are the best reports in Facebook to understand better the performance of the campaigns?

[captnamazing]

I build the reports depending on business case. You need to start organizing the data around your main KPI and a secondary KPI that happens more often and is on the way to your main goal. Then you can start pulling reports based on campaign performance, creative performance, demographic performance, even device type performance..
And you find the trends to identify inefficiencies