I tend to naturally take a middleground between the two techniques you're describing. Rather than throwing my arms down, or swinging them up, I shoot them straight out. Imagine you were doing a dive into a pool. Superman style. I get the full extension and reach from the extension of my arms, which assists my legs pushing me in the direction I'm going, whether its up for height or out for distance. Getting that nice extension in your flip is vital. The more you extend, the swifter your rotation will be, if you tuck well. For the tuck, from there, I allow my arms to circle from a 'superman' position town towards my shins. It's kind of like dunking a basketball in a really high hoop. Reach, then dunk down. See how that feels for you! It works great for me.