The Ojibway understanding of truth is "as much as I know from the place I now stand." I've always liked this definition because it implies a willingness to change, something we should constantly be open to. This also reflects how I feel about my yoga practice and teaching.
The very first time I started practicing yoga (in the early 2000's) I had to drive across town to get to a yoga studio. Now, it seems like there's one on every corner. To say it's a growth industry is a huge understatement. Yoga is estimated to be worth $27 billion US.
There are about 50 different major types of yoga, and more are being invented every day. So, which should you choose? I'm sure you're aware that they're not all the same and you may have even found out that the differences can be so vast that teachers from different types of yoga will contradict each other on seemingly important details. How do you know who to trust?
You may not know that there is no reliable resource to help figure it out. There is no governing professional body to help regulate standards and practices. There's no way of knowing whether the teachers that's trying to turn you into a pretzel has any idea what they are talking about.
The good news is that with the growth of yoga comes an increased interest in the scientific community. Money and time is finally being spent on research that is showing that yoga is in fact good for us, and hopefully this will eventually lead to answers to more esoteric questions like which yoga is better, how often should you practice, etc. Currently, there are no honest answers to these questions.
In the meantime, what I can tell you is that in my yoga classes, I am telling you as much as I know from the place I now stand. I am constantly reading and researching yoga, taking in new training, and trying to put it all into place to give you the best, safest yoga that I can. But the thing I am trying to focus on the most is the part of that definition of truth. "..the place I now stand." This requires that a willingness to change and adapt with new information.
I will avoid jumping on fads that aren't grounded in practices that seem consistent with my education and research. I think all yoga teachers need to avoid being stuck in what's known in science as an "appeal to tradition." That is, having faith in something just because it has a long and established history.
There is a very strong bias to be faithful to tradition in the yoga community. While the drive to hold a yoga practice sacred is well intended, it's important to also bear in mind that as new information comes in we may learn that there are better or safer ways of doing things. If the new information seems reasonable, we should incorporate it into our instruction rather than rejecting it because it conflicts with ancient yoga beliefs. Knowing this and being unwilling to adapt our practice would be doing our students a disservice.
The best advice for picking a yoga class might just be to keep all this in mind and find teachers that you think you can trust who are continuing their education and aren't trying to convince you that their way is the one "true" yoga method. Ask a lot of questions and in the end, listen to your body and trust your own instincts. And do a lot of yoga.