PSP is more impressive from a \'features\' stand-point, but the two have entirely different goals.
PSP = extension of PS2.. essentially a portable PS2 with MP3 playback.
DS = technologically similar to an N64, but with the huge twist of the entire dual-screen concept.
You\'ll get gameplay on DS that you can\'t get on any other platforms, while with the PSP you\'ll gain portable playability of current home-console titles. Both systems have big pros, and very few cons.
I mean, people who have played the DS say that the graphics are fantastic; obviously not up to the level of the PSP but if the gameplay is there.. who cares? DS is.. more or less.. capable of running all of PSP\'s games with diminished detail. It\'ll probably cost a lot less too.