In terms of being really ahead of its time, I think DQIII is one of my favorites, in fact it might be my favorite 8-bit RPG overall though FFIII gives it a run for its money. The GBA version is nearly perfect finally updating the interface and adding a bunch of side content and adding a new addition to character building creating a deeper overall experience.

DQV I felt was the most well rounded entry and probably has the best story even if I felt it was a little forced in some parts and lacking in other places but I really enjoy Mon-Games so the combat was really fun. This all helped by the DS version which fixes most of the problems with the original version (interface, graphics, sounds, rate of monster joining you) so it has moved into being one my favorites.

DQVII I feel is the last DQ game I truly loved overall though I haven't given IX as much of a fair shot as I should. What the plot lacks in drama or compelling characters it makes up for in being clever with an overarching plot and series of events that are really interconnected but not very apparent to you until after the fact. It also has a really cool Job class system and the monster system and town building are pretty epic in this game and the most well thought out in the series. If only the pacing was better...