I know that I might get a semi-biased answer posting this on a Nintendo based website, but I thought I would give it a shot.
I'm going to be flying across the country this June. I'm going to be in the air alot as well as layovers in airports. I am thinking about buying something to keep me busy.
The both have probably the same amount of games that I would love to play. DS has a better price point of course, but I'm not a huge fan of the touch screen. Maybe it will be better if I play a game that uses different ways. I have only played Brain Age and watched my g/f play Trauma Center. PSP has better graphics and I love the ability to watch movies. I was told that you could watch movies on a DS, but at the time I didn't know that the DS had a removeable memory slot.