I have to say, having both, I like the PSP a lot better. God of War, Joan De Arc, FF7 Crisis Core, Metal Gear ect. There are just a lot more "adult" games for the PSP and they're a lot more current (as in they look like PS2 games rather then N64 games). The DS isn't bad, and does have a few games I like (FF4 for instance) but those are probably going to the PSP as well (there are multiple FF remakes for the PSP too).

The main thing I like about the PSP though is the other bonuses. I can stream music and movies (and some games ) from my PS3. I can transfer movies and PS1 games onto it from the PS3 and play them without needing a disk. I can make Skype calls on it for free when I don't want to use my cell phone minutes anywhere there's Wifi.

The PSP brings a lot to the table both in games and in functionality. Unless you have a PSP already I would def recommend it above the DS. After I got my PSP I haven't used my DS once (in over a year).

   Crisis Core alone is worth the purchase.  That game OWNS.

Um that was only FFI and FFII. After that square enix made the DS their main focus. So I wouldn't count on FFIV coming to the psp.

This thread answers the OP quite nicely

http://www.neogaf.com/forum/showthread.php?t=222049

I am 31... and love the DS... You should get one.

It has the widest range of games of any console on the market. There is something for you.

I have 3 DS and use it at the same time.