I'd go with a DS, myself. Or better yet... hold out for the 3DS.
http://e3.nintendo.com/3ds/
http://nintendo3dsblog.com/
It's backwards compatible with the DS, and will probably fully overtake Nintendo's portable development plans within the next year. So, if you're looking for a new portable to keep up with the times, I wouldn't purchase a DS so close to the end of its developmental lifespan. I'd wait for the 3DS and maybe pick up a GBA SP (only $25 - $40 around here) to tie me over until then... but that's just me.
