I like the lava rock with a little spag for potting oncids and phals. It stays "moist or damp" without staying "wet". Finer media stay wet down underneath the root mass and that is what rots them. And orchids grow slowly so we don't know something is wrong until too late in the game. If you plant in spag or fine bark, don't water until the pot and plant are really light in weight. Then water.