I'd say you've picked a winner on both systems, especially given some of the upcoming titles for the PSP.
I own a DS and it is LOADED with good JRPG titles, however most of them feel a little bit cheap, and if you dislike Tactical RPG's you won't have that many choices available.
In terms of traditional/unique RPG's for the DS I can recommend the following...
- The World Ends With You
- Mario & Luigi: Bowsers Inside Story
- Suikoden: Tierkries
- Final Fantasy IV DS
- Chrono Trigger DS
- Dragon Quest V
However the PSP has some really impressive looking RPG's on the horizon, so if you can only pick one, I'd think about your own personal taste in JRPG's and wait on it, because if half the awesome JRPG's out in Japan come out for the PSP, it'll be a hell of a system to own and I'll likely be buying one myself.