Here is an interesting article. You may not agree with it. It compares steel, titanium, aluminum, and carbon fiber as frame materials and concludes that aluminum is the worst due to low fatigue endurance and its being subject to catastrophic failure.
http://talu.com/materials.php
From the article:
"Aluminum has the worst fatigue endurance of the different metals commonly used in bicycle tubing. Therefore, aluminum bicycle frames are sometimes designed to be jarringly stiff in order to avoid fatigue failures and to give the aluminum frame an acceptable service life. So much material must be used that aluminum frames may not weigh less than steel ones. Aluminum is also subject to catastrophic failure, so extra material must be added to provide an adequate safety factor."