Thank you Rob and Rasqeo for your insight. You inspired me to take a closer look at all three.
As you say, CGC offers the most structure and guidance, starting at beginner level. If I'm understanding correctly, it is also the only one of the three offering live interaction, grade exams or level-appropriate technical challenges. There's even a summer camp in Massachusettes (which sounds amazing). Not surprisingly, most expensive of the three at first glance, but my impression is the cost is inclusive for all the online features, and if one wants this kind of content, guidance and interaction, it's the only game. Depending on how well these features are implemented, seems like a bargain. I don't know who runs the live performance seminars. The live coaching staff is listed. There's a 7 day trial and 30 day guarantee.
What's most unique about artist works is Jason Vieaux of course, as well as other celebrities teaching other styles and instruments, which, depending on how easy it is to switch or engage with different courses, could be a great feature for some people, but I don't know if that's even possible. If one wants online lessons from any of these people, it's the only way, but I've heard concerning things about the turnaround time. For what it offers, it's a bargain, but not for everyone, and not for beginners that I can see. No trial/guarantee I can find, so about $100 to try?
Tonebase looks like the least inexpensive at first, but it seems the interactive video-exchange sessions are an additional charge per session, and I cannot find how much they cost. Per-session charge could be a plus for some, minus for others. If the instructor roster rotates, is it impossible to stay with the same teacher? Not for beginners. 7 day trial and 30 day guarantee.