You can use Pasmo and Suica cards anywhere; it doesn't matter which card you hold. The main difference is the provider of those prepaid train cards: Suica is from JREast, and PASMO is from non-JR Rail companies in the Tokyo Region, such as Tokyo Metro and Toei. Though the difference is the PASMO card can be used to store day passes; therefore, if you plan to use day passes, PASMO might be a better pick.