I'm surprised there isn't a thread about this already.
Which do you prefer: PSP or DS?
And as a mini-question
Which are you going to get?
Personally i'm obsessed with the PSP with now. The DS, while it's innovative, the second screen doesn't seem to benefit it much. The only real things i've seen it do is show a map (which you can just easily press start and show one) and act as a steering wheel.