For N64 emulation, RetroArch uses a libretro core similar to Mupen64Plus. However, you can download core emulators to play games on various platforms (PC, cellphone, console).
RetroArch is a graphical user interface front-end, not technically an emulator. The game is loaded instantly and most of the Nintendo 64 games run seamlessly on this emulator. The game must be installed on a microSD card to play it. What you get with MegaN64 is a good N64 emulator, very great and very user friendly. MegaN64, a tweaked version of Mupen64 Plus, is by far the most popular emulator on Android, with more than 900,000 reviews and an average user rating of 4.6.
Mupen64 plus is a wonderful emulator free emulator open source emulator supported by several OSes that can support many choices for gamer who are interested in playing N64 games on their systems.