If the PSP had touchscreen then it'd been the best portable console ever, since it has not only homebrews like msn and scummVM (if i remember correctly), but every emulator and just everything. While PSP has the DS emulator, the DS can't emulate the PSP, since the PSP is way more powerfull. (And that's why the DS battery lasts longer)
Just watch the technical specs:
CPU: PSP CPU (1-[b]333 MHz[/b])
[b]64 MB Main Memory[/b]
4 MB embedded DRAM
Display 4.3 inches (16:9) full-transparent type, TFT
[b]480 x 272 pixel, Approximately 16,770,000 colors
Every function, every game, everything!
Obviously this is just my opinion, because I had a PSP and it is the funniest console to play.