IMO, here is what makes DS the best deal:
A. It's cheaper.
B. It has some amazing games that you can't play on any other console, like EBA, and Phoenix Wright.
C. The PSP is in a gaming drought(ask a psp owner like StrategyKing), while the DS is in a boom, with many, many new games being released for the system all at once.
D. Japanese support for the DS is unprescidented.
E. Games like DQIX are real, big budget games, stolen from consoles that are REAL, and not handheld games.
F. First party Nintendo games, like NSMB.
G. Touch screen controls, microphone, and dual screens make the system unique and fun to play.
H. 3rd parties are flocking to the DS, like Activision with Guitar Hero, Tecmo with Ninja Gaiden, and others, while the PSP is, once again, losing support from 3rd parties.
I. Full backwards compatibility for the GBA, which has lots of great castlevania, Nintendo, and rpg games, like Fire Emblem, Golden Sun, and the like.
J. Games don't lose value. They resell for just as much as you paid for them, due to the format that prevents abuse of the game itself.
K. System is well built and not delicate. Won't drop when you break it.
L. Type of games. If you are a sports gamer, the PSP if likely more you cup of tea. If you like Japanese games, RPGs, SRPGs, and just cool, quirky, or music games, the DS is for you.
M. A full fledged exclusive Zelda game is on the system. Same for mario, Ninja Gaiden, and Final Fantasy tactics.
N. Most to none of the DS games are ports. Most higher rated PSP games are, like Castlevania, sports games, or FFTactics.
O. More people own a DS, so the online is more populated.
P. The DS is very popular. You'll be owning the undisputed winning console in ever area, arguably.
Q. DS games you buy now will be BC with the next gen DS, most likely. It is unlikely the UMD format will last.
R. Many PSP owners keep their PSP in a drawer. Most PSP owners already own a DS.
S. The DS is a craze and will be remembered forever as a revolution, like the Wii.
T. The DS has cheaper games, equipment, and more stuff you can buy for it, due to this popularity and supply of games available used, while that stuff maintains its value longer.
U. Cartridge format is awesome. Fantastic. You can never scratch or ruin games, and you'll never get a bad game. You can buy used games with no fear.
V. UMD's are relatively fragile.
W. If these:
1) Buttons are very small and the L and R are a little tricky to press in fast paced action games
2) Playing online can be a pain if you need the Nintendo Wii Fi adapter
3) Not as durable or immortal like the old Gameboy
4) Even with a wide and high quality library, the amount of shitty games can discourage you
Are the only reasons not to buy one, imagine the things left off there that are reasons too buy one.
X. The PSP has many flaws also, that I won't get into a flame war to reveal.
Y. Phoenix Wright: Ace Attorney exists and is worth the price by itself. Same can be said for Elite Beat Agents, and Hotel Dusk. These games are classics. Just look at some of the avatars around here to see that.
Z. When's the last time you saw a MLB:08 The Show avatar around here?
Meta A. MP3 player, graphics, Monster Hunter, and pirating sell the PSP. Most PSP owners will tell you it's not worth owning one unless it's cracked. The PSP is currently in a huge game slump and most PSP owners admit it won't end. The PSP2 is rumored to be right around the corner. The old PSP games that are rated highly are largely PS2 ports or PS2 type games, with very few new PSP games coming out. The controls on the PSP are bad, including a frusterating analog stick, which pales in comparison to a touch screen. The PSP isn't innovative, and relies on a GBA type gaming console, with no backwards compatibility on top of costing more money than the DS, a system which is superior in virtually every way. Despite the PSP's old lead in metacritics rankings, that lead is closing fast, and the DS will pass it. Not to mention that the PSP list is stacked with redundant sports games that are virtually unplayable considering the newer versions are released, while the DS list is amazingly diverse, and games like Phoenix Wright, and most great casual games, aren't even in the top 80 percentile. The DS is getting, real, significant 3rd party games like DQIX, while no third parties are willing to invest major fanchise numbered games like DQ, FF, or even first part God of War on the PSP. You don't get God of War 3 on PSP, you get a spinoff. You don't get a FFVII remake on the PSP, you get a spinoff. You don't get new mainstream IP's on the PSP like Professor Layton, Elite Beat Agents, or The World Ends With You, and I defy you to give me a PSP release list worth a crap, when I can list you an upcoming DS game list that will make you drop your shorts, like the new Grand Theft Auto game, new games from Suda, Square, a NEW castlevania game, tons of J and S rpgs, new games from bioware, Atlus, EA, Capcom, Activision, and virtually every single developer on the face of the planet. The PSP list is unforgivable.
Nobody will tell you the PSP is the best console this gen. Many respected members like myself and several mods will tell you the DS is the best system Nintendo ever released. Ask them. Look at who posted in your topics. Look at who thinks what about each system and count the fanboys just putting in votes for Sony/Nintendo verses the true believers. Could a PSP owner make claims like I have? No.
Meta B. Battery life is unbelievable. PSP's is lackluster unless you buy the bulky and hated second/ultra bettery which costs even more money.
If that doesn't convince you, then you deserve what you end up with.
