Only the first one is really worth playing for that. NIS has never been able to top the original trio. Disgaea 2's cast is boring (I kept hoping Adell's
good guy thing was a massive troll that would deliver an epic joke in the middle of the game, but that never happened, so he was just reduced to the lamest of the lame in the end). D3's cast is somewhere in-between.
Although, maybe Atlus being the localizer is at least partially responsible for the first one being so good in this regard.