>>27616808 or arguably 5 (on the DS). If you liked either of those play 4 (NES or DS (which is missing party chat), 3, and maybe 9 (though it's a different beast altogether). If you like the series, play 1 taking into account when it was made and that it was one of the first games of it's type at the time. Then play 2 if you're still into the series. And if you really want to play more DQ, play 7.
If at any point you feel like you want to play though them again, I personally suggest this order
1, 2, & 3 on GBC, 4, 5, & 6 on DS, 8, and then optionally 9 and 7 on their respective hardware.
