Fins

From research it appears that stiff fins are the best provided the diver has strong leg muscles.  If the dive is extensive the below fin is of poor design as it can make the diver's muscles tired.

The recommended designs for fins are curved fins, as it produces more of a thrust, like the ones below

or split fins, the design produces more forward motion with less stress, the diver will need to kick faster when against a current unlike the curved fins.

New fin design is the Aqualung Slingshot this fin has bands with can be set at different levels, it releases its energy before the upstroke to give an extra boost to the diver essentially an added boost of power to the divers kick.

Boots must be wore with adjustable fins unlike the slip on fins.

http://www.scubadivingfanclub.com/Diving_Fins.html