here's what I think.
Try a PSP, Honestly, there is a reason why only 12% of PSP owners own a DS, because once you go PSP, you won't go back. ;)
PSP give you PS2 graphics on the go, if you are a HUGE Metal Gear fan, go with PSP..
if you want to play same games you played on GBA (or GB for that matter,), a game with almost identical engine from 10-15 years ago, Buy a DS and get your Pokemon Pearl. ;)
Uh, yeah, where to start. It's great that you like your PSP and all, but the DS does far more than the GBA, and the Pokemon games run on a 3D world engine, and a much better resolution 2D engine in combat. It's hardly the only game on the DS worth buying either. Say what you want about the PSP, and present support for your argument, but don't talk crap about a system you don't own and know nothing about.
Btw, if only 12% of PSP owners own a DS, then that means 5.5% of DS owners own a PSP... didn't quite think that one through did ya Genius. You also definitely don't want to get into a discussion about sales paterns determinging quality, because more than just the clear hardware advantage the DS has almost twice the attach rate of the PSP, which has the lowest attach rate in recorded video game history.