Both samurai and knights served a higher person than them. Samurai served a shogun, and they were required by bushido to live and die in the service of their leader. Knights served kings and lords. Both samurai and knights were not paid in money, but instead were paid in land grants.
Knights and samurai are more similar than different because they are paid the same way, have similar leaders, both use a wide variety of weapons, and both developed feudalism around the same time.