I do none of the above.
I use some basic polyphonic versions of game music, which switches depending on the emulator menu currently being run. For MAME I have a fast techno track from Dancing Stage (DDR), then for SNES I use the Mario World music, Megadrive the Sonic music, Game Gear the Shinobi music, Gameboy the Tetris music etc.
Works for me, and the music kicks in quicker cos the file sizes are small!
I always liked the Killer Instinct attract sequence music too, which I sometimes use for MAME. I think lyrics or actual music ruins the arcade experience.