The DS: If you think about it, what could you possibly use the touch screen for other than a menu or a map? It has a bunch of really cool things on it (the touch screen, the built in microphone, the pictochat, wireless play ect. ) but Nintendo doesnt make much use of their special products, like the E-Reader and GC's online abilities. It has no good games out yet and wont have for quite a while. Lastly, Pictochat is a useless joke.
The PSP: Just like the DS it has no good, or for that matter original, games out yet. People try to defend it by saying stuff like, "But it can Play DVD's and play MP3's", they just keep going on and on about its special features. Yes I know, its very shiny and stuff, but what about what it was built for, playing games?! All Sony did was take their PS1, slap on some cool features and realese it. Then they realized they should make some games for it so they remade a few and rereleased them.
Basically the problem with both systmes is that they have no good games, yet, although Ill put my money on Nintendo to make the better games, which most everbody will dismiss as kiddy games just because theres no major violence, cussing, or sexual themes. The PSP will most likely sell more than the DS though just because people dont care about the gaming aspect and think that its uncool to own a DS.
If you want a handheld that has truly good games, buy a Game Boy Adnace.