NVIDIA Shield Portable

Below is my quickie rundown of how well the NVIDIA Shield Portable emulates classic consoles.

NES: Great
Gameboy: Great
SNES: Great
Genesis: Great
Gameboy Advance: Great
N64: Good – the Shield hardware is more than enough to run the games, the emulators available are the problem.
Playstation/PSX: Great
NDS: Good. Some lag in parts, but nothing too bad.
GameCube and above: Poor – games are unplayable

tl;dr: The Shield Portable is best handheld emulator console out there.