Agreed, you would find a mount made of pine to be all but completely disintegrated in a year or two. Hard woods are best, especially pieces with knots and twists. These tend to last many more years than a straight branch, but it also depends on the species.
David, I agree with all the above, but would like to add a word of caution. Most, if not all, pine have a resinous substance. Any wood that is resinous is not recommended for orchids, unless it is treated, the same with woods that are high in tannin (mopani for instance).