Hi,
I do use vidoes to do my yoga and I use B.Kest, Eion F., and Shiva Rae. For about 2 months, I did Magically Hips every other day because I herniated a disc in my back. (That is really how I got started on this consistency with yoga.) Springing from a seated position to a plank is great for the core. On days that I do an upper body workout, I like to do B.Kest Sweat because it focuses a lot on controlled movements. I think that Shiva's Fluid Power has given me the most insight into engaging my core while doing yoga, plus those routines really require you to engage the core. Overall, for me, she is the best. I am always the most open and flexible after doing some of her sequences. She's very yogaish and not for everyone. After doing so much yoga, I really believe that you have to do quite a bit of yoga to really reap the FULL benefits of improved tone and flexibility. It is easy to go through the motions of yoga, but it takes time to get to a point where you can really work a pose to your edge. Any yoga or even stretching, is still better than none.
Tracy