Besides what’s been already said, I would add a suggestion, from my own experience.
think of any course, studies or project you’ve been involved with, and ask yourself:
(1) Are you good and more efficient at following a steady pace, and enjoy getting specific tasks and exercises and homework from teachers?
Are you a bit at loss and lacking self-discipline when you have to make your own schedule, and plan steps towards a goal?
Then structured courses are probably the best choice for you.
(2) Do you prefer to do things your own way, tend to get annoyed when people tell you how/what/when to do things?
Are you able to motivate yourself enough to reach your goals?
And/or do you naturally prefer to work/study alternating short periods of time of very intensive activity and full rest, rather than “a little bit every day”?
Then, the non-structured challenges are probably the best choice for you.
I hope this helps!
p.s. I’m type two, so I did fine with basic subscription and challenges. 