Thing is, it's all about what you'd rather have in a handheld. PSP has some great games coming out, but it's mostly more serious, 1-player stuff. DS is mostly about connectivity. Me, I'd rather play with some friends and such, but PSP is fantastic for single player.
If I can, i'll be getting both.
By the way, you said the final fantasy series can't be continued in numbers for a different company than Sony? Wrongo. Japan has FFIII out, and most likely more to come.
It comes down to this. Would you rather play Mario Kat, or Need for Speed?
Yesh, i'll ened up getting both if I can, as I like any type of game all around. I just know that DS is popular with my friends, and connectivity is more fun than single player, for me.