The emulator of choice should be no$gba, because it emulates gba and nds near to perfection. You could think about buying the shareware debugger too, that works like a charm
About gba, you could try VisualBoy Advance too, that comes with nice debugger.
Another emu for nds I use is dualis, but is less accurate than no$gba.

Last, if you want a perfect look about your game working, you need some real hardware