The PlayStation port is the real version of the game. The GBA version has been reworked a little due to new content but the real issue is that the US version is buggy and can give the player some unfair advantages, the DS version is a revamped hard version but this is largely to give old fans a new challenge and to compensate for the new customization system. The PSP version appears to be based on either the iOS version or the Advance version (specifically the PAL Version which fixes the ATB bugs in the US version) so it should be close to the original in difficulty but retains some of the reworking due to retaining some of the Advance versions special features.