As far as I can tell, the only worthwhile emu on PSP is the gbpsp one, and is also one of the only emus compatible with more recent custom firmwares (5.xx)
but it's a GBA emu that runs 99.9% perfect. All games I tried so far worked perfectly, even two oddities (Mother 3 patched and F-Zero Climax(mode7 game))
It's frequently updated by jap developpers. I guess the frequency is what makes it good, since the SNES emu stopped being updated a while ago and it can barely run games at an acceptable speed. I never thought I'd see a GBA emu that runs better than a SNES emu. Also, NES emus aren't compatible with recent CFWs

Also I'm pretty certain N64 emu is sorta a novelty, not something you'd be able to enjoy all the time (ie bad framerates, glitches, etc) But yeah, I guess it does work
i do emphasize that gbpsp is a godsend