Good advise from "jsehorn"! Just remember what works for jsehorn in his environment might not work for yours, if you have a nursery anywhere close by you can ask them or other orchid hobbyist in your area to see what works for them, a good place would be a local orchid society.

Personally I use medium grade for all of my orchids that are not mounted and make a my own mix on what I have learned works well for those that are in pots. I don't add sphag to my mix. I have as many mounted as possible with the amount of orchids I have, repotting every 2 years would take me forever if I did not mount.