Rather than thinking about what is "best", I think what you should consider that the substrate you use goes hand-in-hand with the care you have to give. They aren't separable. I like to use a well-draining, low CEC, inorganic mix. Doing so increases aeration, reduces the risk of overwatering, reduces soil compaction, and gives me more control over the availability of fertilizer. But that also means I have to fertilize and water much more frequently. If you add organics you tend to increase water retention, increase CEC, and decrease drainage which, in turn, changes your watering and fertilizing regimen. So instead of thinking about the "best" mix (that always causes these threads to go down in flame wars), think instead about what would work for the care you can give in your environment. In the dog days of summer in Houston (zone 9a), some of my trees need to be watered three times a day.
People grow trees successfully in many different substrates, but you'll find people reluctant to make a recommendation to you because your success with their mixture depends on variables outside of their control. Namely you and your local climate.
Scott
