Let me preface this by saying that I just finished reading a post from last year where my mom was scolded for wearing a tank top to yoga class and it still fires me up. Above all, no matter what you choose to wear, you should feel safe where you practice yoga. If the studio is judgmental of your clothing, find a place with better energy that knows what's important in life. Now, onward.
For me, choosing what to wear to class comes down to three things:
1. What kind of yoga am I doing? I personally find wide leg yoga pants annoying in hot yoga classes but fine for restorative classes. Lots of layers don't make sense for a Bikram class, but will keep you warm during a yin class.
2. Do I feel comfortable? Make sure you cut any itchy tags off ahead of time, and stretch a little to see how the clothes feel when you move.
3. Do the clothes work in common poses? Some low riding pants may dip lower than you want if you're in a squat, or your shirt may ride up in down dog. Test out the poses and see how it works for you.
PS- I have a lot of yoga mats, but this one is my favorite.