What is your favorite report and why? (Aka I'm training a new Director of Development with no Tess experience)

Hey!

The title says it all!  

What is your favorite report and why?

What is the most useful report or tool for you and why?

What do I absolutely need to make sure this new person knows that might blow their mind (or not, that is cool too)?

Any info you would want someone to teach you coming into a new CRM?

You guys are the best!  

Cross posted on other forums!