Re: Most stable neck material?
as far as non-natural, definitely graphite or carbon fiber.
as far as natural, a multi-piece laminate with alternating grain directions.
as far as single woods, any sufficiently stiff, dense wood will make a good stable neck, especially if using a nice straight grained quartersawn piece and likewise if baked.
and of course, any of the wood ones can be made even more stable with the addition of stabilizing graphite rods.
single expanding vs double expanding truss rod makes no real difference to stability, but there is a huge difference in adjustability.
mind you, just because it's extremely stable, doesn't necessarily mean that it sounds good.