The question is really simple.
If you wanna have a handheld with many free and good application, games and tools as well as a nice and friendly scene, go for the GP32.
If you have too much money and wanna have quite the same a bit more powerful, but less emulators and stuff (and wanna give away your money for it), go to the Zodiac.
If you wanna play games only and don't care to waste time, go for the GBA or PSP. You can't compare both to the GP32 or Zodiac, because they are (will be) mainstream and it will be used up to 98% for games only.