Bark is the "standard" medium of choice for planting orchids. It's not "the best", but it's workable. Some people add sphagnum, perlite, coconut husk or coconut shell chips. Basically anything that will allow a mechanical hold on the
plant, and doesn't rot too fast. Since orchid roots ae so sensitive to rot, the medium has to be kept airy, and be allowed to drain and dry rapidly.
THere's also another technique called "Semi-Hydro" that is being used by a lot of people. more info here:
www.firstrays.com