from what I've seen the o3ds XL is just not fast enough to emulate many gba games (like the battle network series)
if you have CFW, you can inject to vc, that's the best way, as it runs at full speed, even though that's not really software emulation. (no save states, no sleep mode, extracting Saves is a pain, etc)
I've heard that gpSP's cia version gives better performance,
but I'd say if you have a little extra cash getting a DStwo is the way to go, it's like an r4 flash cart but has a built in extra CPU, it can emulate GBA and SNES games very well,
with the GBA emulator, you get:
- 'Emulated' 60fps,
- Real time clock! (great for pokemon rom hacks, and for rockmanexe 4.5!)
- Uses a standard save format, (easy transition from emu to 3ds)
- Supports save states
- Supports sleep mode
- dsTWO works on any 3ds version, as well as DSi/dslite/dsPhat, not hacking, modding or CFW required.
The downside is it cost about $40 :-/