My Boy is a popular GBA emulator out there. It has high compatibility along with a laundry list of features. They include superior link cable support (over WiFi or Bluetooth), high game compatibility, fast forward and slow down modes, cheat codes, and hardware controller support.
It also has some advanced features like OpenGL rendering, BIOS emulation (so you don’t need a BIOS file), and rumble emulation using your phone’s vibrate motor. It offers an almost complete experience and that’s impressive.