mounting orchids what is the best material?

They all work. What you use depends primarily on your conditions (humidity, how often you water, etc.) and what the plant requires (need to dry quickly vs. never dry out). For example, a plant that needs to dry quickly might be on a stick or piece of cork with no moss, but a plant that shouldn't dry out might be in a wood basket with lots of sphagnum moss. Initially you may have some trial and error for your conditions. Another factor may be availability. If you have access to appropriate twigs/sticks/bark from your back yard you may not need to buy anything.

FYI, another consideration is how much moss, if any, to cover the roots on a mount. I have warmer, dryer conditions than many so I probably use more moss on a mount than someone in more moderate conditions. On some species, even in my conditions, I don't use any moss on the roots.

 

Many woods will quickly rot. I wouldn't use pine, fir, Douglas-fir, willow, birch, etc. Where you live you probably have access to oaks, hickory, pecan... Ask someone local what available materials are rot resistant. I use oak and manzanita because they are available, and also cedar fencing boards and redwood scraps because I have some laying around. I know some folks like blueberry twigs, grape vines, sassafras... lots of options.

 

There could be pests in the wood depending on what it is and where you get it. For starters, don't use any wood that is showing any signs of rot or fungal activity and preferably nothing that has been on the ground. Some people say it needs to be baked in the oven to kill pests. What I do is select dry, seasoned wood and lay it in the sun on concrete for a few days. In my climate that will kill any insects or eggs. Probably doesn't kill fungus spores but they are ubiquitous anyway. I collect a small stash to get me through the winter.

I have been leaning toward cork for most because it lasts so long. I use local small sticks often for miniature creeping species (ie. Schoenorchis scolopendria) and larger branches (2" diameter or larger) for large heavy species such as large Dendrobiums and Cattleya. It is largely a matter of preference.

FYI, don't use ocean drift wood because of the salt content. Lake drift wood is OK.

 

Tree fern will keep mounted plants moister than cork. A lot of grapevine will rot quickly unless it has been pruned back to the same spot many times. So the larger branches and root of grape hold up well. I'll disagree with Kelly on one thing. Douglas fir bark ( not the wood) holds up really well. Lilac and citrus wood also works well.