Generally Sitka Spruce is considered the best wood for building masts because of its high strength per pound. Hollow spars generally are lighter for a given stength and so are preferable to solid spars in most cases. Box Spars are the easiest hollow wooden spars to build and result in a pretty good strength to weight for a wooden spar. They give up quite a bit from an aerodynamic stand point.
In small boats, (under 20 feet)wooden spars can be quite comparable in weight to the normal run of the mill aluminum spar but as rigs
get larger woden spars quickly become substantially heavier, less strong and more flexible than aluminum.
The down side of wooden saprs is that the glues have limited lifespans, and they can look perfect on the exterior and rout out from the inside. Their greater weight reduces stability and increases roll angles.