I'm inclined to think the fibreglass option might be too flexible and the aluminium one is very dependent upon how the two sections are joined. Maybe filling the fibreglass version with spray foam would improve things?...
I was once gifted a fibreglass windsurfer mast that had been stiffened up for application as a dinghy mast by filling it with concrete. It certainly was stiffer until I chopped it up with a disc cutter!
Wood is good!