I bought a PSP just over a year ago, and think it's a great little machine. The biggest advantage I've found is that I can play games without having to interrupt usage of the TV (that makes the PSP wife-friendly)... The DS Lite was released here in australia on the 1st of June, and while my interest in the DS wasn't great, the DS lite really caught my eye. In part, I can blame Cabel's three great little DS Lite reviews at
http://cabel.name/ (he is also responsible for some great Mac software too, btw).
Anyway, as far as which to go for - well, if I had to choose one, I couldn't decide.
The PSP is great for the PS2-style games; Burnout Legends is amazing, Wipeout, Ridge Racers, etc all very good too. Lumines is an incredible puzzle game, which could be on any platform. It also has a reasonable number of sports titles (my favourite being NHL 06). Plus, if you get one that doesn't have the newer firmware(s), you can play a whole range of homebrew stuff, like (s)nes emulators, mame, scummvm, etc.
The DS Lite has an incredibly bright screens compared to the DS - they're pretty comparable to the PSP screen, possibly a bit brighter even. It's a smaller unit, it's really easy to stop and start your gaming by closing/opening the lid, the games all load/save incredibly quickly, since it's a cartridge based system instead of a disc one like the PSP. I've only had the DS Lite for about three weeks now, but the games are *FUN*. It seems to me that the fun factor has tended to disappear from a lot of gaming in recent years - all of them seem to be a re-hash of the same games that came out last year, just with better graphics, better sound, and sometimes better gameplay, but certainly not always. I've played Metroid Prime Hunterrs on the DS Lite, which hands down is the best FPS that I've ever played on a console (though I still prefer the mouse controlled PC versions). I also bought New Super Mario Bros, and it's just amazing. It's fun, bright, addictive and keeps you going and going. A great difficulty curve too - it's pretty easy at first but gets increasingly difficult as you go, but not frustratingly so. Super Mario Kart is a must for any old-time SNES owner. If you liked it then, you'll like it now. I've not checked out the homebrew status much with the DS, but from first glance it does appear that the PSP is a little ahead of the game there (no pun intended). However, you can get Linux of the DS, if you want to install linux on yet another electronic device
![Headphone Smile :) :)](https://cdn.head-fi.org/e/headfi/smily_headphones1.gif)
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All in all, I think that they're both great little machines, and it probably comes down to your preferences in gaming. If you like fun quirky games that rely on good gaming design over super-flashy gfx/snd then the DS lite is probably the one. If you like 'darker' gaming, and you reckon that the world revolves around sports and car racing (after car racing after car racing) games, then perhaps the PSP...