This is just my opinion, but it is based on having owned bikes built of differing materials. Steel has a distinct quality that is hard to define. My best attempt would be to say that it does everything very well, but not superbly. It's lifespan is forever if you don't let it rust. Aluminum rides like a truck. It is just so stiff and jarring. A carbon fork will help a bit, but not much. One of the nicer bikes I have owned was a Colnago Dream that was full aluminum. I finally sold it because I couldn't stand the ride. Carbon rides a lot like steel, but it is stiffer. Will it last? Who knows. I bought a Colnago C50 after I sold the dream and it is a very sweet ride. Which brings me to my favorite material. Titanium. My Litespeed does everything superbly. It is stiff yet rides well. It has about 30,000 on it and still looks new. These are my observations and I realize that everyone measures comfort differently. However, aluminum would be my last choice in a roadbike frame.