First problem: You're on a mac. All programs that are made for windows, then ported to Mac's aren't going to be very good.
Now, I can't guarantee these fixes will work, as I'm pretty sure these are the default settings, but let me read off my settings for my VBA. (Also, VBA is the best GBA emulator out there, so a replacement emulator is going to be hard to find.)
For video, you're probably going to want to resize the window to be x4 times the size, on VBA-M (Which I think is Windows only) they can resize to x6. It'll probably look blurry at that point.
Now, you want to go to tools > Filters > and pick either Normal or Simple x2. For me, there's little to no noticable difference, and mine's set to normal by default. This will make the graphics better. You can experiment around with the filters if you don't like the blocky look, but for a game system like that, I think it works best.
For audio problems, go to tools > sound > and down to near the very bottom. Pick either 22 KHZ or 44 KHZ. I think 44 KHZ sounds better, but in most people's mind, it adds far too much treble and sounds weird. Try either of those. If it's on 11, though, then that'll be why.
For choppyness, you'll want to set the frame skip. This will make the emulator not take up too much space when running and will make it run smoother, however, the more frames you choose to skip, the less smooth it will look. So, you'll want a good balance. Normally, automatic will be a good judge of this, but if you're not too sure that it's right for your computer, change it to 1-3. If that still doesn't work, set the throttle to 100%. If your game runs fine with these other settings, setting the throttle will make it run odd. Only run the throttle if you absolutely have to.
If it still doesn't work, then maybe your computer just isn't powerful enough to run it.
Also, Axle will want me to say this. Don't download ROM's, they're bad.
