BROs, since there are a lot of "which emu is the best for X platform" posts in this thread, I've decided to prepare a simple FAQ which I plan to include in the Opening Post (tm).
tl;dr version - recommended emulators by platform:
NES: Nestopia or Retroarch-Nestopia
SNES: Retroarch-bsnes/Snes9x-Next cores
N64: Project64 & retroarc-Mupen64Plus core
NGC/Wii: Dolphin
GB/GBC: Retroarch-Gambatte core
GBA: VBA-M or Retroarch-Next Core
NDS: Retroarch-Desmume Future Core or vanilla Desmume
SMS/GG/GEN/32X/SCD: Retroarch-GenesisPlusGx Core or Kega Fusion
SAT: SSF or Yabause
DC: demul or Nulldc
PCE: Mednafen
PS1: Mednafen or epsxe or PCSX-R
PSP: PPSSPP
PS2: pcsx2
Todo: C64, Amiga, Atari XL/XE ST, NeoGeo, Dos, etc.