Quickest path to deco diving?

[Subcooled]

Well freedivers dive 100m with 1 breath (that is 200m and have to fight against buoyancy as well in the first half), so it is clear who is more efficient based on your criterion .

A competition freediver is an athlete with highly tuned technique and absolutely no unnecessary oxygen consumption.
Efficiency is world class then, but there are some hard limits, too. Distance is limited to 100m or 200m.
(OK! Herbert Nitsch went to 253m and came back alive, but it really wasn't a success, was it?)

Give such a freediver a small neutrally buoyant air cylinder, and you'll witness perfection in S.C.U.B.A!

 

[Subcooled]

Agree, but they are not going as fast as they possibly can either. They find the optimum pace to utilize the gas at hand.

I have to agree with this. I am not a keen freediver, but I have done some amount of pool freediving. I've found out, that if I want to dive 150 feet or 165 feet (my record), I need to relax and control my speed. If I dive too fast, I can't get far. The hard physical fact is that twice the speed means four times the work/oxygen consumption. Hence, with twice the speed I will only get half the way. There is a base oxygen consumption too, so slowing down indefinitely doesn't work, either. There certainly is a sweet spot.