Right if you prefer puzzle games and platformers go for the DS,
If you prefer racing games and swish visuals and just an all round platform go for the PSP.
I have a DS and I'm somewhat disappointed with the amount of "childish" games being released for it. Only really looking forward to mario party, hardly ever play it. Would look into a PSP if I had the dosh.
I know the PSP's battery used to be rubbish but the DS' is quite good, I dont know about the new PSP.
I'd go for the PSP if you have the cash