It depends on the application. For frames, I'm a big fan of carbon fibre but not all CF is the same just as not all steel or Ti or Al frames are the same just because of the material used. The manufacturing process and design contributes more to the feel of the bike than the material. I will admit that based on past experience I am partial to steel and CF frames with Ti coming in second. I would not turn down an Al frame but I don't generally gravitate towards them initially.