I'm replacing my front door. Should I go with fiberglass or steel?
My primary concerns are security, durability, and low maintenance.
The decision between fiberglass or steel depends upon your application.
With a high-quality door, you'll have a longer-lasting (a green choice), lower-maintenance door and avoid the downsides of fiberglass (warping) or steel (rusting).
eHOW provides a good write-up.
For more information:
Read Christine and Robert Boles's Q&A "Where can I find eco-friendly exterior doors that will match my historic home and keep the cold out?"