Wii section's weird, moved to general since it's going to talk about a few.
Anyways as far as portable systems go, there's better than the PSP in the form of those Dingoo/etc. handhelds, but even the latest models aren't as cheap as a used PSP, and they have some of the same drawbacks (low resolution, etc.) so many people go for android if they need portability, though getting a device with good controls means you'll be reading a lot.
There's also consoles, the Wii's emulation library is pretty well-developed, the PS3's more powerful but doesn't have as much development life under it's belt so which emulators work better could be a tossup.
Human vision is logarithmic, it's not linear. And nits doesn't tell the whole story of perceived brightness. OLED'S look brighter then LCD's even when both are set to the same nit values because of the higher contrast ratio on OLED's
"And nits doesn't tell the whole story of perceived brightness" it's not about perceived brightness it's about all HDR content in TV and movies being mastered for 1000 nits so it doesn't look right with anything lower, it's also about dynamic range
OLED's can get away with a lower peak brightness and still provide punchy HDR because of their contrast ratio. Like I said human vision is logarithmic. The higher the peak brightness the diminishing returns in perceived brightness.
@The Real Jdbye Oleds hit around 750 nits nowadays. The difference between a 1000 nit and a 750 nit isn't huge. It's only about a 4% increase in perceived brightness. Not huge at all. You'll need at least 2000 nit displays to notice a bigger difference.