Are we talking JRPG's or WRPG's. As they are typically fairly different.
If we're talking JRPG's I'd suggest Chrono Trigger. I haven't played the DS version, but assuming it's true to the orginal, I think it would be a good place to start. I've always felt Chrono Trigger was a little more easy to get into then most JRPG's. It's paced well, both gameplay and storywise and I think the DS version actually has difficulty settings.