This isn't what you want to hear, but GB is only as good as the person using it. I have some friends that are trained audio engineers and they can make GB sound as good as anything. I do a pretty good job too. LOL!
What I would like to emphasize if you are looking for pro sounding recordings:
-get decent monitors,
-learn to use your microphones AND the space/room you are recording in,
-read up on the art of mixing,
-learn what a compressor does and familiarize yourself with them,
-practice mixing other's songs (Nine Inch Nails has 2 of their songs as free GB downloads for mixing)
-read and practice, read and practice, read and practice, read and practice, read and practice, read and practice, read and practice, read and practice, read and practice, read and practice, read and practice, read and practice, read and practice, read and practice, read and practice, read and practice, read and practice, read and practice, read and practice, read and practice,
and that about covers it. Garageband is just a tool. You have to make it work.
Good luck and welcome to the forum! If you have any questions, feel free to ask. Lots of smart people here.
X