The Classic Reports are kind of Plain 
The modern reports are more colorful, maybe a little flashier.  The downside to the Modern Reports is creating these reports can take a little more time.  Classic Reports let you choose fields in order choosing the fields from left to right or top to bottom.  The Modern Report Wizard, on the other hand, populates the fields you choose in alphabetical order.  I have provided a variety of reports - classic and modern - that you can Clone or Copy to make it easier to modify an existing report.