Here's what I can tell you about bicycle frame materials. In the low to mid-price categories, the question is basically steel or aluminum. Aluminum is only 1/3 as dense as steel, which means an aluminum tube will weigh only 1/3 as much as a steel tube of the same size. Since aluminum is only 1/3 as strong as steel, the tube diameters are larger than they would be for steel. The net result is that an aluminum frame winds up being lighter and stiffer than a steel one. Steel does have some advantages over aluminum, however. It has greater fatigue strength, which means it can stand repeated high-stresses without failing. Steel is also easier to repair if you ever wreck your Bicycle. Braze-ons for attaching racks, fenders or water bottle cages can easily be added to a steel frame, but not aluminum one. For mountain Bicycles, which have shocks to cushion the rider & reduce the loading on the frame, aluminum seems to be the material of choice for the vast majority of riders. In road Bicycles, aluminum also holds the edge, but by a much narrower margin. Though lighter, many cyclists think aluminum frames are too stiff, and prefer a steel frame which can flex a bit more. On a personal note, I have always ridden steel Bicycles & been very happy with them.