Ok so I did a test. I went into a flat world tp'd myself so I looked up at a 25 degree angle, and used each rocket without changing the angle, I flew in a straight line. This is very slow once decending, but can show us an accurate estimation of how much of a difference eacht duration makes.
Duration 1: 348.769 blocks = 348.769 blocks/gunpowder
Duration 2: 426.148 blocks = 213.074 blocks/gunpowder
Duration 3: 463.582 blocks = 154.527 blocks/gunpowder
With this test, duration 1 is obviously the best. You also don't have to spend 3 gunpowder just to fly 100 blocks when using duration 1 fireworks.