tubing. A long thread on what frame material is better led to this article that is an objective view of the material strength. Great for geeks, while others debate (endlessly) whether a steel, aluminum, titanium or carbon fiber bike is better.
Anyway interesting reading, it shows essentially, that steelis the most dense between aluminum and titanium.
Also says that for a given density (e.g, same construction), then the stiffness of aluminum and steel are identical (would not have thought that) Also, that the stregnth of the latest type of steel (Reynolds 853) is greater than aluminums and nearly that of Titanium.
Basically, it used to be that steel was heavier for a given stiffness, but with Reynolds 853, this isn't true. Titanium particularly the high end 6Al-4V beats everything, but is super expensive (40% stronger than Reynolds 853 and same stiffness). The last disadvantage is that steel does rust and does fatigue, so has a theoretically shorter life if you ride like a maniac.