I don't know much about Great Books. I only know what I learned at their website . I have heard some good things. But I don't know that working with larger groups would be an advantage. Many of the benefits of Lit.
Circles come about because of the intimacy of the group.
Also, leaders of Lit Circles are often trained leaders having attended training sessions in their use. Lit Circles if done properly do require a procedure, as does anything else you do in your classroom. These are two different approaches. I don't know that they should be compared as one being better than the other. Thanks for the emails on Junior Great Books.