If we're talking about just the games, I would go for the DS. It has a ton of great games, especially if you import all the nice Japanese games that have little chances of coming out in English. Plus it's portable, so it's nice to bring along to play wherever and whenever.
If we're looking at all of the features of a console in general though, the PSP would also be a good choice for the added media playback capabilities, even if good games are a lot harder to find for that system.
For me its PSP cause its the only console i have . Yugi OH GX - is probalby best game for it I have. PSP has all I need when I am on road you know 1gb memory stick + Share Steno CD211 with 80gb HDD as a backup is really good thing when you are traveling somewhere.