No$GBA
I have the no$gba, but I have some issues with it:
1) As far as I can tell, you can only have the same ROM loaded on all emulated machines
2) The parallel support driver fails to be installed every time I try to do it so that I can link my laptop and my desktop together for emulation that way; and
3) The battery state files are incompatible with other GBA emulators, so I cannot import those states into no$gb
If there is something that I am incorrect about, please, let me know here, I'd love to be proven wrong so I can learn.