i had a hacked ds lite for about a year while traveling, the lite doesn't have web browsing built in, you gotta buy a cart for it from europe. although i hear the dsi has it built in now. i haven't hacked the dsi, but the ds lite was super simple, and you could do pretty awesome shit with it. my favorite was a comic book reading program, i ended up reading more comics on it than i did playing games. but yeah, from everything ive heard you get more outta hacking the ds than you do the psp. plus, if you're interested in web browsing, it's waaaaay better on the ds than the psp because the ds has a touch screen so you can type web addresses and write really easy as opposed to the psp which requires you to scroll through the keyboard with the dpad (pain in the butt).
although it's been a while, i still have the impression that there is a SHITTON more homebrew for the ds than the psp as well.