DS for a few reasons.

1. It has more RPGs than anything ever.
2. There is definitely something for everybody, from the near-impossible random dungeoncrawling variety to touchscreen-controlled combat games like The World Ends With You.
3. It has remakes of all the best RPGs from the NES and SNES, and random new games from long dead franchises like Lufia.
4. The only non-Japanese release of FF3, meaning it is also the only system that can play FF1-6 and Chrono Trigger.
5. It's portable and has a very long battery life, so you can clock in some RPG hours on long bus or plane rides.
6. You can touch the screen. For games like RPGs that rely heavily on menu selections, that ends up saving you hours.

DS has quality, quantity and variety (speaking of RPGs). Sure the PSP has much more potential but the developers aren't using this potential. Between Phantasy Star Portable 2 and Dragon Quest IX/FFIV/Golden Sun DS I would choose DQIX, Golden Sun or FFIV any day.

Dissidia is a 3D fighting game, not a RPG.

DS - and there's really no arguing it.

That said, I'm not very fond of many RPGs on the DS, so to me it's not really my favorite RPG-machine right now, but it's still got more than any of the others, and lots of them high quality.

X360 hands down. It's got more WRPG's than any other console (Fable 2, Mass Effect, Risen, Venetica, Divinity II).

It depends on what kind of RPG you like. DS has a lot of RPGs.
If you're looking for a console I recommend X360. It has Lost Odyssey (I great JRPG that reminds me of the old FF, even the music is composed by Nobuo Uematsu) and Mass Effect. The PS3 also has some awesome RPGs, Valkyria Chronicles and Demon's Souls to name a few.
If you're a turn-based RPG whore like me, I recommend buying a DS. It has lots, lots of JRPGs.

Playstation 3 will top them all for teens but for adult wii might be the one...I think

@Hisiru- i will agree with you that the PSP has alot more potential then the DS that the dev's simply aren't taking advantage of overall just yet... however...

Dragon Quest IX/FFIV/Golden Sun,  is all a matter of opinion, same goes for my phantasy star portable 2 post earlier, the dif is though i've pretty much seen what the DS has to offer graphiclly, its decent but a does not come close to what PSP is capable of, and to be honest i also give PSP more praise then the DS for the simple FACT that the PSP is the only handheld to not only SURVIVE against a Nintendo based handheld gaming device but its also taken away quite a handful of exclusives that COULD have been DS exclusive but since PSP is around that didn't happen.

For Example, if it was only DS, chances are Phantasy Star Portable 2 would most likely be Phantasy Star DS 2, but again, since PSP is around THAT did not and WILL not happen.

Anyways, i hate monopolys, and nintendo has had its crown for far to long when it comes to portable gaming, and in MY opinion, i feel Sony has done portable gaming better then the Nintendo has done with the DS this gen, im not saying the DS is bad, just PSP is better for various reasons, exclusive games like PSP2 being one of those examples. along with Crisis Core and Kingdom Hearts: Birth by Sleep and many others.

I couldnt disagree more with that bolded part. Monopolys are there for a reason and the reason why nintendo holds a monopoly is because they are the only developer that can differenciate between handheld gaming and console gaming.......the PSP is just a gimped ps2 and as such will receive gimped ps2 games while the DS will get games that will not fundamentally work unless they are on the DS. So what exactly has sony done better than nintendo in portable gaming this gen?

Nintendo rightfully should hold the monopoly over handhelds because I can guarantee if another company held it with the same mentality as sony (where handheld gaming=console games) than for sure handheld gaming will die.

Pfft, i respect your opinion dude, however i strongly disagree with you, no one deserves a monoply, no one, the PS2 was great but even it went way over-board, Original Xbox should have gotton more shine and Gamecube should have been FAAAR better then what it actually was.

i don't believe in 1 gaming platform > all others, you can if you want, but just remember, the one who controls over all can ask for any price they want for there games and products, tell me, do you really want that? because i don't which is why i'll continue to support the PSP more then the DS yet still enjoy what the DS has to offer nice and fairly. *tips hat* good day sir.

Are Nintendo handhelds overpriced?