I haven't ever really played PSX games but for DS games from most favorite to least favorite:
1.
Super Mario 64 DS-Comments: Even if you got every star in Super Mario 64, there's new things and it's still a very fun game.
2.
New Super Mario Bros.-Comments: Can't go wrong really with this game. Again it is ultra fun.
3.
Metroid Prime Hunters-Comments: It's more fun when it's portable. For a FPS game, it's quite addicting. Only problem I ever had was my hands got tired after playing 1+hr. of intense multiplayer combat.
4.
Pokemon Diamond-Comments: Not as good as the 'ol Generation I/II games, but still fun for a DS game.
5.
Animal Crossing: Wild World-Comments: More fun when you have friends to play it with. If your into less hectic style of gameplay, I suggest this game.
All of these games I got for my DS and played for a long time, and had good experience with them. Hope this helps.
