“Which form of therapy is most effective for manic depression?”

None of them. No psychotherapy has ever been shown to directly help Manic-Depression which is now called Bipolar Disorder. Bipolar Disorder is a purely biochemical disorder that only responds to medication. The only role of psychotherapy in Bipolar Disorder is to help people with Bipolar Disorder cope with having a severe mental illness.

See this link..
https://www.ncbi.nlm.nih.gov/
pmc/articles/PMC2575757/
or
https://www.nami.org/Blogs/NAMI-Blog/April-2019/Different-Types-of-Therapy-for-Bipolar-Disorder