Emulation on the gp2x is nice but thats all there is. The screen on the psp is nicer for movies, the sound is better and at least there are commercial games available.
The gamepark scene has pretty much peaked, less and less is getting released and there hasnt been anything "wow" in long time.
I have both now, but my gp2x has been gathering dust. I was playing the DS the most but lately I have been playing the psp more than I did now that there are finally some decent games for it.
Can't say I've seen much development regarding homebrew on the PSP either lately -- a slow/unplayable Playstation emulator is pretty much it... and oh yeah, a way to boot homebrew on 2.80.
Devhook doesn't support firmwares above 2.71, so you won't be able to run games requiring those if you downgrade and plan on using it (apparently, the author's more interested in playing DS games than developing it further
)