There's around one or two alternatives to Retroarch for most main systems, I have GenesisPlus (not the Retroarch build) and Realboy right now that I occasionally use, and there were 2 SNES9x ports to the Vita that weren't a part of Retroarch, mGBA is the GBA/GB/C emulator you're thinking of as well.
But Retroarch is pretty much the "premiere" emulator setup nowadays, I don't think there's a lot of reason to not use it beyond maybe being a bit more complicated to setup if you want to change a few things for whatever reason.