First off, I have a PDA that runs the latest Opera Browser. I have a PSP with the 2.71 firmware. And I have a DS Lite.
With my PDA, everything loads fairly fast, and always is accurate to the actual site. I have a Flash plugin, but that being said, when you try to view anything large in Flash, like a YouTube video, you get poor results. My PDA, by the way, is one of the most advanced dedicated PDAs out at the moment.
My PSP also has Flash, however you get very similar results, making it particularly useless. Especially considering there's a limited amount of RAM, which usually won't cover a terribly running YouTube video, anyway.
Going off of what's been reviewed with the Nintendo DS Browser, you will get an overall poorer web browsing experience when compared to the other two. The PSP does have a larger screen, but of course the touch screen really help the DS. I suppose in this aspect, it beats the PSP browser. However, it's hard to justify the DS Browser when a PDA will beat the pants off of it.
That being said, the DS Browser is a brilliant tool. Dual Screen viewing is incredible, with the smaller version of the site on the bottom. It's brilliant, something that I wish was offered on my PDA.
I still recommend picking up the DS Browser, even if you've got a PSP or PDA. For two reasons: 1, it's far more practical than the PSP browser. 2, it's pretty damn cool. Seriously, it's a sleek browser on the greatest handheld ever made. Why not pick it up? If anything, just for email and bragging rights.
~Dac