I like the Rocket Chinese Course.
Interestingly, I can only give 5 stars, if I try to click higher than that, it defaults to no stars...
I very much enjoy the energy the instructors have. The level of progress for each lesson is well done. You learn quite a bit with each lesson, and the audio is engaging. But you don't get thrown so far into the deep end that you get frustrated and quit. I is a very good balance between enough old (to prevent frustration) and enough new (to prevent boredom.
I also interacted with the customer service once. It was a very good experience. They took my feedback and incorporated it in the very next update. They also addressed my (user created) problem. They were prompt, and kind, and very helpful.