I've only played DQ I-III and VIII, I enjoyed them all although I probably couldn't go back and enjoy the earlier ones so easily nowadays.

VIII was really wonderful, it gave a nostalgic sense of exploration that I rarely feel playing current JRPGs. It might be my favorite DQ game.

Really want to play IV-VI and VIII someday (heard VII is REALLY long, one of the longest cRPGs or something?), and looking forward to DQIX.