I've taken several classes and have learned from each one of them. The quality of the instructors has been very good in my experience. There are free classes that you can sign up for. I would suggest trying one of those first. IMO the best of those was the 2013 BOM. Once you sign up for a class it is always available to you and you can go at your own pace. The instructors are not available for questions for the free classes, but they do answer questions for the paid classes. There are printable instructions you can download for each class and you have the video with the instructor demonstrating the technique. My favorite classes were the Civil War blocks taught by Kaye England (Repiecing the Past: Civil War blocks, Then and Now) and the Traditional Blocks Made Simple, taught by Anita Grossman Solomon. Both instructors have very different styles of piecing, but I learned a lot from them and I have been quilting for many years. Ann Peterson also has a class on quilting big quilts on a small machine. I learned a lot in that class also. Leah Day is an excellent instructor for free motion quilting and has couple classes on that, I think.
One important thing about Craftsy is that they are very quick to refund your class fee if you do not like the class. I received a refund for a class on color that was not what I expected. The classes that I have liked I have watched several times. I am currently making the Arrowhead quilt from Anita Grossman Solomon's class.