The prominent astrologer, Noel Tyl, has said that Solar Arc Directions are the most successful predictive technique, and I agree with that, but I have not finished my research into tertiary progressions.
I use SAD to find what most people use Secondary Progressions for. Simple prediction. I treat SAD the way others seem to treat Secondary Progressions. I use secondaries too, but they offer less action and are insufficient for the amount of predictive information that I seek.
By comparison, Solar Return charts have not impressed me very much, so I have gradually drifted away from that method.
My astrology career had two phases. The first phase started when I was fifteen, and it amounted to me reading every astrology book I could find, but I didn't know about any metaphysical bookstores, so most of my books then were pop astrology, except for Astrology A to Z by Llewelyn which was not very good and not very helpful. I had Sun Sign books and very little else except Edgar Cayce. I really liked Joseph Goodevage's Write Your Own Horoscope, but it was not as comprehensive as I wanted. But I always searched the local bookstores whenever I found one.
Then I met an old man at the Unitarian Church who was a Theosaphist, and taught me a few lessons, but I don't think he was that knowledgeable. He was just an enthusiastic Theosaphist.
The second phase of my career happened when I moved to a town that was loaded with good astrologers, and there was a great metaphysical bookstore where local astrologers gave classes at night in the back. I bought books and I studied hard and I bought a computer and computer software from Matrix and Rob Hand. But I was so skeptical of predictive astrology that I just ignored it for a long time and concentrated on natal astrology.
Then one day I resolved to take a course on predictive astrology from a local astrologer who had a university degree in astrology. She had traveled to England to attend a school there, and she is one of the few astrologers I have met who had an astrology degree.
I thoroughly enjoyed her course. It amazed me. She taught mostly Transits, Secondary Progressions, Solar Arc Directions, and Solar Returns. I was very lucky that she was enthusiastic about Solar Arc Directions.
Then I learned cosmobiology, and they use transits and SAD almost exclusively.
I launched my research. I was determined to discover which, if any, of these methods actually worked. I had expanded my understanding of planetary pair meanings and synthesis, and that was key. I bought many biographies to use as laboratories for astrological testing. I remember reading a biography of Jane Fonda and tracing her life events with prediction. That's when it became clear that SAD and transits in combination stood out beyond the rest.
I have used SAD for years, and I feel very lucky that I found that method.