The results you get mostly depend on whether you have the o3DS or n3DS and if you have a kernel hack or not.
For o3DS without kernel: Most emulators are rather slow. Not all are though.
For o3DS with kernel: Most emulators run at full speed.
For n3DS without kernel: Most emulators run at full speed.
For n3DS with kernel: Almost every single emulator runs at full speed.
As for SNES and GBA, without kernel on o3DS you should use blargSNES and without kernel on o3DS there is no good way to play GBA games at the moment.