Whether you choose Lava, Haydite, Kanuma, or something else, the most important consideration in choosing a soil is drainage. You want a mix that will provide a good balance of air and water to the roots. Too much air and the roots will dry out too quickly. Not enough air and the roots will suffocate.
We recommend our lava/bark mix for an all-around great choice. You can use this mix for accent plants, pre-bonsai, and bonsai alike, both indoors and out. The roots colonize a pot long before the particles break down. We have been using this mix at the nursery for years and our plants thrive in it.
Some people like to customize their bonsai soil, and so we offer different ingredients as well.