https://www.cyclingnews.com/features/best-gravel-bike-pedals/
https://www.cyclingabout.com/why-flat-pedals-are-better-than-clip-in-pedals-for-most-people/
make sure to read my resource on how to select the best flat pedals for your needs.
https://www.cyclingabout.com/best-flat-pedals-for-bikepacking-touring-commuting/
Most data suggests that at a constant power rate on a constant road gradient, there is no discernable difference in efficiency between flat and clip-in pedals (study 1, study 2).
GCN recently tested the efficiency of quality flat pedal shoes vs clip-ins – watch this video to get the full scope.
The results were really close, especially given the test subject wasn’t accustomed to riding with flat pedals. The biggest difference in power loss/gains between the two different setups is when sprinting out of the saddle.
I suspect the results may have been even closer if he dialled in his flat pedal technique.
https://www.youtube.com/watch?v=aVLfqjcTbnU&ab_channel=GlobalCyclingNetwork