I'm sure others will have different opinions and I'm not a Yoga expert but an experienced Iyengar Yoga instructor recently told me that Iyengar teaches that the "downward dog" pose is considered to be the single most important pose. (Iyengar is mostly a static-type yoga that holds poses for flexability and strength.) She went on to say that if you are in a hurry and only have a few minutes for your daily exercise simply hold the downward dog pose as long as you can. It is a static strenghening and stretching pose that has many of the benefits of other poses she said. Since it's static, it has good application for those with joint problems and anyone in a hurry to do something good for you. She said it is considered to be a mild "inversion" and that if you can hold the pose for 2 plus minutes it has antiaging effects.
If you google it there are tons of pics and info.