ds... i had one 2 years back but sold it, and i regret it everyday.... it depends what kind of games your looking to play.... if your an old school gamer who likes to relive the glory of SNES days gone by, the ds is definitely for you...
get a supercard or a flash card for it... you can download the roms using torrent and play loads of games from the current ds and gba library, which is a LOT of games....
http://wiki.pocketheaven.com/Main_Pagethe games are usually up for torrenting a couple of days after release too....
starfox ds, FF3, Elite Beat Agents and Castlevania had me addicted for a long time....
then again with the ipod touch, you got video, music plus you can upload a gba emulator on the thing, so that even more hours of fun..... i was fooling around with my friends ipod touch a while back and it was the bomb.....