I've had fibreglass, and now I have steel. They both have their advantages, as has been pointed out. Were I a coastal cruiser, I would choose fibreglass for weight, resistance to corrosion and decent looks. But as I'm voyaging, and want to go offshore and perhaps to high latitudes, I've chosen steel. Yes, there is more maintenance, but preparation of the metal initially plus a regular round of inspection and "keeping on it" will take care of that. Ask me about Ospho and two-part epoxy paints.
The advantages aren't readily apparent until you hit a reef or a container, or lightning blows holes in what isn't, in fact, a very good Faraday cage. Then they become obvious.
If you are in Indonesia, on the other hand, with a badly dinged steel panel, you can pay a guy $50 to cut out the old and weld in the new. Stove in a two-foot piece of your fibreglass hull, and your trip may very well be over.
Anyway, I weighed (no pun intended) all the cruiser books I'd read and tried to assess the pluses and minuses of each material next to our intended, and comparatively extreme, use, and steel came up first. If I was to cruise the Caribbean, by contrast, I absolutely would get a cruising cat in fibreglass, even though I've never sailed one. The advantages of cats in shallow, semi-protected waters are evident.
If I had loads of money, I'd probably have a Sundeer done in copper-nickel, which is a rare boat building material, but as has been noted, seems to be the best choice of strength, anti-corrosion and weight of all.