It is always difficult to define "the best". IMO they all do a decent job, some have special tools that could produce some improvements. In my experience defragging is very effective with my XP machines (when needed, once a month usually). With Vista, defragging has never had any significant effect on the speed or shutting down/start operations, actually the opposite is true, I believe this is due to Vista having its own boot device which every 3 days is activated. I like Puran because of its speed, I also have DiskTrix UltimateDefrag 2008 on Vista which is highly customizable, but as mentioned above, I could never perceive any benefits from defragging (also very slow).