Due to weakening demand since the 2008 global recession, ports have had to reconsider how to compete differently to attract new business and new investors. Extant literature mainly focuses on either customer competitiveness or investor competitiveness. This study develops a new model of port competitiveness that simultaneously considers the effect of port strategy on customers and investors. This model is referred to as the “balanced theory of port competitiveness.” An analytical hierarchy process model builds on 10 factors that customers and investors consider important, and it is tested on 12 global seaports. The results show that port managers should consider the effect of their decisions among the factors because failure to do so can improve one factor of competitiveness while harming another. This study tests a theory that explains the behaviour of port managers and provides them with a practical guide to evaluate the effect of their decisions on customers and investors.