The most sustainable wood is wood that is...
- harvested from managed forests,
- travels the shortest distance to the mill,
- uses the least amount of energy to process, and
- travels the shortest distance to the consumer.
Otherwise it's not sustainable.
There are many variables that play a part in making the determination of "most sustainable wood," and for each end user, the results will differ.
For more information:
Read "Which species of wood are the most sustainable?", a Q&A answered by J Neufeld.