You can say what ever you want about steel vs al and all your going to get are those that own AL love it and those that own Steel love it. BUT AL does not have the longer life expectancy that steel will have AND this fact is brought out in " VeloNews Buyers Guide" on page 42 and I copied below for your reading pleasure.
As anyone familiar with beer cans can tell you, AL is softer land less stiff than steel. AL is easy to draw and form into shapes, easy to machine, and relatively easy to weld. Its density is about a third of steel and half of TI, so it is not hard to build a light bike with it. It will oxidize, and should be painted powder coated or anodized to prevent corrosion, but it does not rust away rapidly.
AL has downsides, too. Its tensile (breaking) strength, yield (bending) strength and elongation (the % of its length it can stretched before it’s unable to return to its original shape) are far less than those of high strength steel and TI alloys. AL is more vulnerable in a crash. AL has no fatigue limit, a property that steel possesses, often expressed as a % of its tensile strength. Below this limit, the material can be cycled indefinitely without breaking. This means that AL can be less predictable than steel as to when it will fail after long use.
Back to our beer can: compare a can of beer to a can of olives and it’s apparent that the AL container has much less stiffness than a steel can of similar thickness and diameter. Yet many AL bikes feel stiff. Why? It’s because AL’s density is so low; tubes can be made large and thick for stiffness and light weight.