Nintendo consoles seem to always have the best emulators, likely due to being almost all exclusive games. Every nintendo console recently has had a working emulator before the end of the consoles life. I remember nintendo ds emulators adding support for games that had only just come out.
The other reason Nintendo consoles have the best emulators is because Nintendo generally avoids cutting-edge technology, or at least they prioritise "simple" and "cheap" over CPU and GPU performance.
Apart from the latest consoles (the Wii U and the Switch), the worst-emulated Nintendo console is the Nintendo 64, which also had the strangest hardware (RAMBUS RAM, a general-purpose GPU, etc.)
On that note about the N64, there is a project (created by a friend of mine in college) that is looking to go down the cycle accurate route that the Byuu has gone down with higan.
