Best Online Posting Platforms for Paid Courses

Wowza! There's quite a few platforms for users to post courses for sale online and I am becoming overwhelmed with the plethora of options out there (not a bad thing). Tell me about what platforms you've used either as a small business owner or as a member paying for a course and what worked/didn't. I am currently looking for a few of the best to share with my client to be able to post his courses.