The Tahitian Princess is a former R Ship with unparalleled pseudo-Edwardian decor and as much as half the passenger capacity compared to Rotterdam VI, if you care about ambiance and intimacy.
On the other hand, the service that we experienced aboard the Holland America ship last May was excellent. It was among the few times I can say that a motto is true ('A tradition of Excellence' in this case). Personnel friendliness, overall organization and attention to detail in both hardware and software were excellent.
Whatever you choose, it will be wonderful...