I would recommend beyond a shadow of a doubt that you play the first though. In my opinion, it’s got the better storyline of the two. It may not look as pretty, but it’s still a pretty awesome game.
The second Grandia, which I have on the Dreamcast, was just as good. The battle system was still the same, prooving the old adage "Don’t fix it, if it aint broken!" However, the only downside I’d have to say about Grandia 2 is the voice of Ryudo is done by… Cam Clarke. No offense to fans of Cam Clarke, but I really despise the guy. From Kaneda in Akira, to Leonardo in Teenage Mutant Ninja Turtles, I do NOT like him. Other than that, I really enjoyed Grandia 2.
In any case, they are both great games, though I would particularly recommend the first. =)