This means the current focus of emulator authors is to make their emulators more accurate, which in turn means that optimization has less priority. No emulator exists yet which can play most games properly.
Nintendo ds emulator Pc#
DeSmuMe is recommended regardless of your PC power.
If you're still having a hard time running anything without the output playing like syrup try no$gba. This emulator aims for accuracy over speed but you can tinker with the vast amount of setting to get some extra FPS (see Common Problems and Solutions for tips).