That's like saying is a car made by Honda better than a car made by GM. Are you talking about a Corvette versus a Fit or an NSX versus a Spark? Nishiki made some fine handmade bikes (some even rumored to have been sourced from Colnago). Colnago has primarily stuck with high end bikes but they have sold some lower end bikes (e.g. Colnago Sport) that are probably not as well made and with cheaper components than the high end Nishikis.