For a beginner shooter..carbon..it's straight and takes out the bad arrow ( read ..needs to be straightened) part of the equation when working on form.
for a beginner arrow builder..depends on what stage you're starting from and what tools you have available.
If you're starting from harvesting the material I think bamboo is easier since it's already shaped. Making dowels from a log is real work..not to mention finding a good log to make em out of.
If you're going to buy pre-made shafts, I'd go with wood.
They're more uniform, and you don't have to worry about the hollow shaft.