When you're trying to decide what type of yoga to attend, it's good to know that classes vary tremendously in their intensity and pose variety. Although "Hatha" is a somewhat generic description, it usually refers to a gentle combination of standing and seated postures. Ashtanga yoga is a very specific discipline that follows a set sequence and can be quite rigorous.
One style is not better than the other, but each may appeals to different people depending on their goals and fitness levels.
The Definition of Hatha
Hatha is an umbrella term that means "physical practice," so it's not really a specific style. Technically, Ashtanga is a form of Hatha yoga.
However, many studios and teachers label their classes as Hatha, which has come to mean a beginner-friendly, calming practice. You'll definitely twist and bend, but the offerings in the class are up to each individual instructor.
You'll experience a wide variety of yoga poses in a Hatha class — both seated and standing — but it will likely move slowly and deliberately. Arm balances and handstands don't make a regular appearance, either. It's friendly to just about every level of yogi, but is unlikely to get you sweating.
Ashtanga is a school of yoga developed by K. Pattabhi Jois, a yogi who practiced in the early 1900s in Mysore, India. It's designed around a very specific sequence of postures. Once you've mastered one sequence, or series, of postures, you move on to tackling another series. In all, there are four series, each with a different focus and level of difficulty.
An Ashtanga practice is regimented and requires discipline. Every practice begins with a series of sun salutations and a standing sequence that includes the poses triangle, Revolved Triangle, Side Angle, Revolved Side Angle, Wide Forward Folds, Balancing Postures, Chair, Warrior I and Warrior II. The series on which you're working comes after these warmups and may include forward bends, back bends, twists, arm balances, headstands, binds and other complex poses.
Ashtanga is physically demanding and moves in conjunction with the breath. It flows and requires a high level of fitness. It is the foundation of much of the flowing Vinyasa and Power practices found in studios across the United States.
How to Choose
If you want your yoga practice to double as a workout, Ashtanga is for you. It also appeals to those who enjoy knowing what to expect and measuring progress by seeing improvements and mastery of specific poses. It is very much a sweaty and purifying experience.
Hatha yoga may appeal more to beginners and to people who desire a quieter, more modest yoga practice. It supports relaxation and stress reduction.