Either DQV or DQVIII.

I tend to like them since they are more based around the story rather than a battle system, like VI and VII were.

In terms of DQV, I am a sucker for time travel stuff (though it's light on that front), and the concept of getting monsters, having children, and taking your whole family to kick some ass was very well done.

DQVIII was simply a fun game that knew how to be goofy or dark when needed. I remember some of the boss battles made me feel tension I didn't feel since I was a child. I also loved how the developers stepped up and made the game visually appealing instead of keeping a simple look. Traditionalists freak out that it might compromise the integrity of the series, but I definitely felt like I was playing an old school RPG with a fresh coat of paint on it.

Still can't decide though. So I'll say a tie between V and VIII for now.