What do you recommend as potting mix for dendrobiums?

Have you noticed out of three answers, they're all
different? grin My dendrobiums run the gamut since
I haven't repotted them and they're all still in the
same medium they came to me in. Some in large 'drive-
way sized' gravel. Some in lava racks. Some in wood
chips. Some in sphagnum. One day, I've got to get them
all in the same thing so that I can water them all on
the same schedule.

Tracey