There is a great study in the most recent Undersea and Hyperbaric Medicine Journal called "Evaluation of fins used in underwater swimming" vol.30 No.1 page 57-73 which is the most thorough fin evaluation you will ever see, even better than Rodale's
The US Navy Experimental Dive Unit chose the fins and the research was supported by the US Navy, NAVSEA, and the Navy Experimental Dive Unit.
The fins tested were the Mares Attack, Apollo Biofin, Apollo Biofin with split duct taped closed, Blades, SP Jetfin, Mares Quattro, Oceanic Ocean Pro,and US Divers Compro
So guess which fins performed the best?
And the winner is the splits!
Just kidding, it was actually the Jets it appears on several fronts although the Apollo split fin with the split taped was pretty good too.
One really has to read the study to appreciate how comprehensive it is but some interesting numbers do stand out.
Stiffness: Mares Attack (5.45 N*m2) by a long shot was the stiffest and the Apollo was the least stiff (1.32). The Jets and Quattros were almost the same (1.92 vs 1.95)
Oxygen Consumption while free swimming: The Jets had the lowest oxygen consumption (l/min) of all the fins even better than the Apollos.
Aerobic Velocity :The taped Apollos were the fastest, and the Jets were faster by a little (.77 vs .75 m/sec) than the Quattro.
An interesting quote, "In our studies, the divers invariably ranked the stiff fins as the best and the flexible as the worse, which did not correlate with the objective evaluation of these fins." In other words just cause you feel like you are pushing a lot of water doesn't mean you are moving faster or that you are doing it efficiently. Perception and reality are very different when divers rate fins on how they 'feel'.
I think I read somewhere that many of the Seals were using Apollo Biofins and I can see why especially if one tapes the split closed, but given these guys likely often have to swim long distances and want the most efficient fin it appears the Jet is the most efficient while using the flutter kick.
They did not evaluate the ability to do the various alternative kicks, but those who have used Jets can attest to this capability. It would be interesting to try a pair of taped Biofins with the different kicks as I like their foot pocket much better than the Jets.
The only downside to the Jets I find is like Seajay says the foot pocket stinks and it is this fit which determines so much of the dynamics of how a fin performs. That is why the full foot fins are more efficient than a open heel fin.
I have yet to experiment with different booties for fit but there is one piece of advice I can tell you when buying a pair of Jets. There is huge variation in the wall thickness of the foot pocket which really determines whether the foot pocket remains a box or can become an oval around your foot. The first pair I bought I measured I think 5mm thick and the most recent 3mm. This made such a difference in how they fit that I got rid of the first pair.
A simple way to tell is to try and pinch the foot pocket closed from side to side with your thumb and third finger just above the pins for the buckle. On my first pair forget it, I couldn't do it. On the second not a problem. The first pair the foot box remained a box and dug into the top of my foot and the second the box becomes an oval around my foot. I really think if Scubapro thinned the rubber wall of the footbox down further it would conform much better to one's foot and tranlate into an even better fin. Maybe the military's Jet fin will have this feature.
All in all though a great fin, but a pair of high vis yellow would be great so I didn't have all those technical guys in black swimming into my fins and knocking off their masks.
