Before anything I say, it should be clear that I am biased due to the nature of my business. But my intent in posting isn't to gain business, but to offer some wisdom gleaned from making custom steel bikes these last 14 years.

When i first started doing this (framebuilding), I really wanted to get into titanium as a material for framebuilding. As I researched more and more it became clear, that on the custom end of things, there isn't much to be gained from building with titanium. It is much more expensive on the cost-end for a small-volume builder, there isn't a great offering of tubing for the custom builder, more tooling is required, as well as being subject to hazards I am not willing to be subject to (e.g., obsessively cleaning tubes with acetone before they are welded).

Also, again on the custom side, I found that I can create steel frames that match the weight and ride quality of titanium. Steel tubing is available in so many more tubing thicknesses and configurations than titanium, and for the small/light rider (for whom I build most bikes), that is important.

A Trek 830 is steel, but it is the kind of steel that does not suit a lighter rider well, because it is heavy and thick walled. This means, if you are not big and heavy enough, it will feel fairly dead and not offer a particularly plush ride. A custom builder can custom "tune" a steel tubeset to fit the rider's size, weight, and intended usage. I built an all-steel frame last summer that weighed 2.6 lbs (most titanium frames come in around the 3lb mark). This shocked me, but made me realize the incredible versatility and benefits of steel. Stock steel frames and bicycles, regardless of the manufacturer, will be more "burly" (i.e., heavier and stiffer) than anything custom, for cost and liability reasons.

Stock titanium frames/bikes can work very well for the small and light rider (assuming they fit well), and even overbuilt ones will probably ride quite nicely for the smaller rider, due to the material properties of titanium. It is a less "dense" material than titanium and more "flexy"--often a good thing if you are relatively light. However, as has been noted, even stock titanium frames/bikes exceed the price of identical and often better fitting custom steel bikes.

Finally, aluminum is usually a poor choice for smaller/lighter riders, especially stock aluminum (and there are very few custom builders who work with aluminum, but that is another topic). The reason it is not great is it tends to be very oversized in diameter, and the triangles on a small frame become very small, enhancing the rigidity of the frame and tubeset. This makes the bike, particularly in small frame sizes, usually exceedlingly "stiff" and a harsh ride. The reason aluminum is so popular for stock bicycles has to do with economics much more than it being the ideal or proper material for all bikes.