I've owned a PSP for about 10 months now, a DS for about 4 months. So while I may have some bias toward the system I had longer, I would have to go with the PSP. I'm very much a nostalgia gamer and love playing revamped remakes, and Jeanne D'arc was simply the best handheld game I've played all gen. GoW and CC:FF have been keeping me busy as of late and there's been no shortage of great gaming on the PSP as of yet for me. The PSP, at times, replaced my consoles as my gaming choice at home.

That being said, there has been no shortage of great gaming on the DS at all, and I seriously doubt there ever will be in the near future. So far, it has been the best of the two for on-the-go gaming. Elite Beat Agents probably being my favourite of the type, there are countless others that well suited that void. And to be fair, I havent yet played as many DS titles as I have PSP.

Of course, once FFIV and DQIX come out, I will be saying the exact opposite.

I don't have either, but I really want both. :'(

The games I'd get:

DS: Phantom Hourglass, Pokemon, Electroplankton (if I can find a copy), Professor Layton, a few advanced games I missed

PSP: Daxter, MGS: PO+, Patapon, God of War: CoO

All of a sudden im seeing the tide turn towards PSP

*fixes*

I love my DS. I love pictochat. I love it's games.

Pokemon Diamond, Mario Kart, Animal Crossing, Starfox, Advance Wars, Electroplankton, Phantom Hourglass, etc.

I love Nintendo games.

DS. God do I love that little guy.

I have both handhelds and i must say that i much prefer handhelds over consoles, but if i have to choose which handheld has the best games on it i would say psp even though the game library is smaller, although graphics isnt all, it vastly improves the psp experience, the only thing i dont like is loading times even on the new slim and lite, it ruins the experience a bit on some games for me. The ds has some games i do like though, but my playing time vastly favours the psp, lately theres been soo many great releases on it too.

DS games are much better then PSP games hands down, PSP is great for the emulators for playing my old games on the go though, PSP has a lot of mediocre games the PS2 had even though they get high rankings by review sites usually I can have ten times the fun with my DS games.

DS for me seems too have way more choices too choose from.

I used Game Rankings average score to categorize PSP and DS games. It is very close, and in my opinion PSP has a better library by a little bit:

Like Leo-J said, go to any review website, here's what you will find.

DS has MUCH more games in total than PSP.
But

PSP has more 80%+ games than DS
PSP has higher rating average.

What DS has, is more games, I suppose when you have tons of shovelware on the shelf, it does give the illusion that it has better games.