Sorry, GBA/Snes emulators are really bad on the DS ( which is what you will be using for homebrew even on the 3DS ) and barely acceptable on the PSP.
Believe it or not, I'm still playing GBA games every day, because I have a relatively short trip to work and I found DS/3DS/PSP games too complex for short gaming sessions.
So I stick with my GBA SP2 and a M3 perfect Mini SD. Perfect compatibility , RTS and absolutely zero slowdowns or frame skipping.
That's the only way to go for me.
I'd really recommend you to try to get a real GBA, it's small, it's sleek, batteries almost never run out and plays 100% GBA games you know
Besides, what kind og GBA Temper would you be without a GBA
?