If someone tried to compile all the styles of yoga being practiced, past and present, including the offshoots and burgeoning schools of thought, that list would be non-exhaustive. The truth is, there are so many subcultures within the culture of yoga itself that it's difficult to get everyone together and decide on standards. That why we choose instead to embrace everyone's differences and celebrate the variety of styles created and espoused in this world. That being said, you can't just wear the same outfit for any class. You have to be aware of what a particular practice entails and how you can best prepare for it by way of being properly attired. Otherwise it would be like wearing football shoes to a basketball game. So here are some basic pointers to look out for when practicing certain styles.
Bikram Yoga and Hot Yoga
We all know that yoga practiced in heated rooms are designed specifically to make you sweat buckets. We advise you not to torture yourself too much by wearing cotton pants or thick tees to class. Building up that kind of heat can actually hurt you and your practice. For better or worse, the best kind of Bikram yoga clothes are those that expose as much of your skin as possible (while maintaining the boundaries of propriety, of course). This helps cool the sweat off your skin right away, so that you're still getting all the benefits of heated yoga without dehydrating yourself unnecessarily.
Ashtanga is a rather austere practice, and one that requires a lot of movement in different ways. The nice thing about this is, like Bikram, there is a set sequence of postures so that you know what you'll be getting yourself into and can take that into account when choosing your outfit. There are some poses, such as Bhujapidasana (Shoulder-Pressing Pose), wherein you place the back of your knees on top of your upper arms. If you were wearing shorts, you would be slipping, or you would need to place a towel in between. On the other hand, poses such as Garbaha Pindasana (roughly translated as "embryo in the womb" pose) require you to slip your arms through your legs while in Lotus Pose (Padmasana), so you need the lubrication of your sweat to get them through efficiently. You either need to roll up your pants for this, or consider wearing capri or cropped pants so there's still some sweat there.
Vinyasa Flow or Hatha Yoga
Other types of yoga don't have a set sequence, so you really need to be prepared for anything. Vinyasa classes will make use of a variety of poses that will include, at any point, twists, inversions, backbends or standing balancing poses. Fortunately, these poses are fairly flexible for any type of yoga wear. Hatha is a much gentler style but will also go into similar poses or asanas. Consider what makes you comfortable when you do your Sun Salutations (Surya Namaskar), and base you clothing decisions on that. Shorts, cropped pants, leggings, or slightly flared yoga pants will do just fine here.
Kundalini Yoga or Jivamukti Yoga
And then there are the types of yoga that put much more emphasis on meditation than movement, or at least an equal balance between the two (yoga, of course, can itself be defined as "mediation in movement"). You may move around a lot, but the poses may not be as strenuous, although your mileage may vary. The infusion of music into yoga makes for a very free, very peaceful practice, and you may wear clothes that are similarly flowy and comfortable. Loose pants and simple tank tops help impart that liberating feeling you'll get after these classes.
Now as we said, these are but a few suggestions for the vast range of yoga styles out there. There are yogis who can do their practice comfortably no matter what they wear, but if you can afford it, or if you're interested in a particular type of yoga, we recommend that you look into that best yoga wear that can make the most out of your journey.