That is a great question. To a casual observer they do not look that much different but the body movement that brings you up is very different.
The back deck roll is simple, watch the video after you read the explanation. You torso, paddle and arm sweep as a unit out on the surface of the water till you actually can slink up almost laying on the back deck of the kayak. This is one way to get your body over the kayak without using much body movement or force. In a sense you have gone from tucked forward to standing up body position which lays you up on the back deck. NOW that you are up on the kayak laying back you will need to sit up quickly and take a stroke or it would be just as easy to continue and roll over back in the water. LAYING back on the back deck reduces the force FROM THE PADDLE or AND THE body movement needed to get the boat upright IN THE OTHER ROLLS. LAYING BACK OR STANDING UP IS NOT THAT COMPLEX.
This method does have its critics however. But it works and one could make the argument it could be the fastest to learn. I MYSELF WITH MY BIG LONG TORSO UP SET THE BALANCE OF THE KAYAK WITH ALL MY WEIGHT LAYING OUT ON THE BACK DECK EVEN IF IT IS ONLY FOR A SECOND BEFORE I STAND UP
The twist and slice roll harness's some body movementS that ARE almost magical in what it does. YOUR TORSO ROTATES and leans back only slightly. You paddle slices (not grabbing resistance) These two factors add up and you will be surprised out how you can pop up. I really like the advantages of this roll and generally feel that it is worth the little extra time one may need to invest into learning it. I think it is a little harder to learn this roll on ones own. The hip snap (as in the C to C) is not the major factor in bringing you upright. There is a real sweet spot. Though these roll look similar THEY ARE NOT. ONce you feel the difference you will understand. OF course I think all instructors should learn them all. This takes time. Then they can judge the advantages of each easier than if they stick with one.
But generally I think discussing which roll is better with someone that only does one roll is a bit like discussing politics, religion, or diet. And like lots of things the more you know about a subject the more open minded you become.
Chris Spelius
www.kayakchile.com