There are several threads on the fiberglass headliner.
http://classicbroncos.com/forums/showthread.php?t=270772&referrerid=54418
The main advantage is looks and ability to add lots more insulation. If you are trying to quiet down, control temps better or simply want a better look, it is the way to go. It is also strong enough to mount speakers.
It costs more and is not labor free.
The cardboard or new ABS ones are less expensive, easy to install and retain the classic Bronco look (and performance).
I am having a local upholstery shop make a vinyl one like Nicks Trix, so there is a third option. Sorry to muddy the waters. My big find was my front roof brace was bent and I have some repairs to do before I Lizardskin the interior. Search the forums for that if you have not pulled your existing roof. A common issue for almost all of the old hard tops.
Good luck.