this is a bloody hard question, the GBC was in its time a massive console for homebrew as was the GBA infact the GBA has more quality games than any other homebrew console, the tapwave zodiac, gizmondo and Nokia Ngage fizzled out too quickly so were never pushed to the extreme. the gp32 and gp2x are awesome homebrew consoles but it really has to come down to the Nintendo DS vs the PSP. The DS has the better games and a more varied selection but the PSP has the better emulators and custom firmware providing full speed PSX Emulation.
SO for me the PSP just nudges the DSout of the equation.
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