Coursera used to be great. I've taken several courses in the past. The problem is that most courses were one-and-done deals where they were put up and there was

Coursera used to be great. I've taken several courses in the past. The problem is that most courses were one-and-done deals where they were put up and there was instructor + TA participation during the first 1-2 times the course ran. Subsequently, these courses are still run in zombie mode while users are asked to pay to take them (if you want to do assignments / quizzes). I find their whole approach very unethical since they provide zero actual support for education while charging people money. To contrast, edX will typically run courses 1 - 2x times a year and any time they are run, they typically will at the very least have TA participation although in the 15+ edX courses I've taken, there has always been active instructor participation too. Moreover, by restricting enrollment to 1-2X times a year, it encourages more participation with very active forums and discussions, even when tackling courses that are 4+ years old. Caltech's outstanding Learning from Data course had over 100 replies on many HW discussions despite being run many years after the original edX course (though the most credit has to go to Prof. Mostafa who is an outstanding professor and educator). edX does have other courses that are "archived". Some of these you are allowed to study at your own pace but they are upfront about the fact that you're on your own and more importantly, they don't try to get you to pay them money for a certificate when going through such a course. That is the right and ethical approach imho.