Finding a yoga class used to be simple. You’d walk into your local gym and there would be The Class. Your choices were few because, well, there weren’t that many people looking to get their om on: In 2001, 4.3 million Americans were hitting the yoga mat; just over a decade later, that number has almost quadrupled to about 16.5 million. Studios, gyms, and rec centers now offer an estimated 800-plus styles to choose from, says Leigh Crews, a spokesperson with the American Council on Exercise. Some of it has to do with yoga’s (well-deserved) reputation for being an excellent stress reliever. But a big part of yoga’s popularity surge is it’s just plain good exercise. Virtually any type of yoga improves strength, flexibility, and balance, explains John P. Porcari, PhD, director of the clinical exercise physiology program at the University of Wisconsin–LaCrosse. “The more intense styles can also help you shape up and trim down.”

Want to take full advantage of that powerful collection of benefits? Read on for everything you need to know, whether you are a  first timer or a regular looking to take your poses to a whole new level.

If you are just beginning or want the best mind/body combo, try Hatha
Poses are straightforward, and the pace unhurried. “You do a pose, come out of it, then do another,” explains Mark Stephens, author of Teaching Yoga: Essential Foundations and Techniques. “It’s an excellent style for beginners.” Props like blocks and bolsters are often used to help you get the right alignment. But it’s not just about the body, as your teacher will also encourage you to focus on breathing, relaxation, and meditation (which may involve chanting). And  all of this mindfulness  has a real-world benefit:  A study in the journal Psychosomatic Medicine found that women who practice Hatha yoga once or twice a week recover from stress faster than those who don’t.

If you want to get slim, try Ashtanga Power Yoga
These two provide all the regular benefits of yoga with the fat-blasting bonus of a killer cardio session. Both styles focus on flowing  from one pose to the next without rest—making for a terrific calorie burn (about 500 per hour). “The practice is meant to generate heat in your body,” says Mandy Ingber, the yoga instructor behind Jennifer Aniston’s ageless body. So, yes, you will sweat. A lot. In Ashtanga, the more traditional of the two, you’ll begin with chanting, then follow a sequence of poses (“asanas”) that never changes. In a Power yoga class, the poses vary each time and there’s usually none of the spiritual aspect. A large study in the journal Alternative Therapies in Health and Medicine confirms that women get lean in these classes: Practicing yoga of any kind at least once a week for four years or more staves off middle-age spread.

If you want to chill out, try Yin Yoga
Named for the calm half of yin-and-yang, this style requires you to move slowly into poses (most of them seated or lying down), then stay there for up to five minutes to allow for a xdeeper stretch and time to just, well, be. Not surprisingly, Yin yoga is particularly good at activating the part of your nervous system that helps you bounce back from pain and stress, says Sara Gottfried, MD, an integrative physician in Berkeley, California, and author of the forthcoming book The Hormone Cure. Expect meditative music and lots of attention  to breathing, as well as those centers of spiritual energy known as chakras—all elements that add to the serene allure of the practice.

If you’re prone to aches, try Iyengar
As in many types of yoga, the poses you’ll do in an Iyengar class are traditional. The difference is in how those poses are done. Iyengar teachers are trained in biomechanics, so they understand which positions are most likely to cause injuries—and  how to modify them by tweaking your form and showing you how to use props to make them less intense, says Stephens. Plus, a pause between poses (as opposed to flowing from one to the other) allows you to perfect your position, so you’re less likely to strain something. Iyengar may even help you recover from injury. A study in the Archives of Internal Medicine found that a similar style of yoga, Viniyoga, worked wonders on chronic low back pain in just 12 weeks.

Find the right class: The truth is, you can find a great instructor and class in a church basement, and a questionable  one in a fancy yoga studio. Just keep in mind this rule-of-thumb: Your teacher should be properly trained!