Three major differences between header vs waterfall bidding in programmatic ads are:
Technology - In Waterfall bidding the impressions are offered sequential, whereas for Header Bidding it is offered simultaneously
Revenue - There is no difference in Google AdSense for Waterfall bidding, whereas there is a 50-80% revenue uplift in Header Bidding
Set-up - Waterfall is easy to set up, whereas Header bidding has multiple complexities involved