A question about fins that's not about how they fit

This question stems from the previous fin thread.
Is it better to have a stiff blade on the the fin or is it better to have a flexible blade?

I'd never even considered a flexible blade 'til I read this article about George Greenough and he said he preferred a hard foot pocket and a blade with flex and memory. He modified some old duckfeet to make it happen. He's a knee boarder/mat rider, so the technique is a little different, but the same principles should stand I think. I always figured that a stiff blade moved more water, but maybe the snap is better. Any thoughts? There's definitely a couple guys on here who know something about fins.

 

Thanks man.