Everyone has a different opinion on this. DOCSIS has greater speed, but is shared with other customers. DSL is dedicated to the user, but cannot provide as high of speed.
My verdict: I prefer as high of speed as possible be delivered to me. I currently use Comcast 150mbps internet at my home. It uses DOCSIS technology. I never have seen a decrease in speed from my service. I feel DOCSIS technology works very well and can handle many users regardless of being a shared technology.