I personally hate the 3DS screen for GBA games. My eyes suck too much to play at native resolution, however the scaling from fullscreen is horribly chunky and distorting. I followed Sono's notes to even rewrite the scaling matrix and got better results but still not great.
Anyway MGBA is extremely accurate and runs fullspeed on Switch, which has a far better screen, access to authentic shaders if that's your thing, and can play on the bigscreen. The only downside aside from added weight/size is a small amount of input lag.