I downloaded a few emulators and some GBA ones, but I didn't find anything I liked.
Just for reference, I like the NES FCEUX emulator for the NES.
I'm in a Discord server with the developers of two accurate emulators that I can attest are still maintained:
- bgb (proprietary, Windows and Wine on x86)
- SameBoy (MIT licensed free software, multi-platform SDL2, macOS version has extra debugging tools)
mGBA (free software, multi-platform Qt) is great for GBA and okay for GB/GBC. The author of mGBA continues to accept bugs and test ROMs to improve its GB/GBC emulation. I haven't tried the Game Boy stuff in higan, but it has added SameBoy as an alternate Game Boy core.
I'd like to add that a GTK front-end is being worked on for SameBoy, which would port the Cocoa-exclusive (= macOS-exclusive) features to Linux and possibly Windows as well.