PSP 3000:

DSi:

Here is the latest comparison chart:

PSP 3000

Screen Size: 4.3 inch-display

Screen Resolution: 480 x 272, 16m colors

CPU Speed: 333 MHz

Cameras: Optional with 1.3 megapixels

Memory: Memory Stick upto 16gb

Internet: Wi-Fi

Browser: Yes

Online Shop: Yes(PS store)

Touchscreen: No

DSi

Screen Size: Two 3.5 inch displays

Screen Resolution: 256x192

CPU Speed: One 67 MHz and one 33 MHz

Cameras: Two cameras, both with VGA resolution

Memory: SD slot, doesn't gb memory

Internet: Wi-Fi

Browser: Yes

Online Shop: Yes(DSi shop)

Touchscreen: Yes

Advancements from previous models:

PSP 3000

Better LCD screen, faster framerates, more memory, new mic slot on front of PSP, sleeker, glare-resistant for improved use in outside environments, LCD screen features more contrast and sharper colors, video output now supports interlaced displays, new and improved motherboard and processor.

DSi

12 inches thinner, 2 cameras, bigger in size, matte color finish, both screen sizes increased, better speakers(rumored)

Well there you have it, you be your own judge on which is better.