Maty Ezraty's reply:
My advice to you, as a new teacher, is to be careful about looking for a single solution. I cannot respond to your question with a black-and-white answer. It all depends on the level of the student. What kind of injuries or challenges they are coming to you with? What is the quality you want to achieve from this transition, a soft one or a more vigorous one? There are many different ways to teach this, and one is not necessarily wrong or right. It is more a question of applying the right one to the right situation.
Let's go through this step-by-step.
If a student has back issues, it could be inadvisable to have them take their arms forward by their ears. The added weight may put strain on their back. This is a vigorous and more strenuous way to come up out of the pose. It would not be an appropriate approach to choose with those who are injured or for a beginning student.
For these students, it is best to have them first put their hands on their hips and then come up with a flat back. Coming up with a flat back helps train the back muscles to strengthen. Whether the legs are straight or bent depends on the level of the student's injury or conditioning.
If your students are in fairly good condition, keeping the legs straight is the preferred approach, as it strengthens more parts of the body. A student with hamstring pulls, however, may also want to consider coming up with bent knees. And if having the legs straight causes the back to round, it may be better to bend the knees to come up. The extension of the spine is more important than the legs being straight. Personally, I am not a fan of rounding the back to come up because I do not think it trains the back muscles to work properly, but it does have a nice gentle vibe to it and may be appropriate for certain classes and students.
In general, I do not have my students take the arms forward to come up. Rather, I encourage them to bring the arms to the sides to come up. I find that it is gentler on the spine and more effective on the back and shoulders. Taking the arms forward is very challenging and demands that the back be strong.
When you understand the heart of the issue for each student, you will then be able to choose the right approach. Don't let this be daunting, but rather see that this is the art of teaching.
Maty Ezraty is co-creator of the first two Yoga Works yoga studios in Santa Monica, California. A former YJ asana columnist, she travels around the world leading teacher trainings, workshops, and yoga retreats.