What is the best way to increase leg flexibility?
All good answers. In addition, two things to keep in mind: 1) to increase range of motion (ROM) it’s important to have the milieu of the target muscle(s) warmed up, and, 2) stretch to the point of tension, not pain. Most programs can be effective. There are certainly a wide variety. I know of no research that suggests that one method is more effective than another. Just do it.
Take care.