https://hydrogenaud.io/index.php/topic,120370.msg993351.html#msg993351

Let's start with MP3.
MP3 is very old codec and has some flaws. It was designed for music (stereo) at mid-high bitrates.
It doesn't support multichannel. They tried to fix it with "MP3 Surround" but it failed.
It doesn't support lossless. They tried to fix it with "mp3HD" but it failed.
It sucks at low bitrates. They tried to fix it with "mp3PRO" but it failed.

Let's start with AAC.
It supports multichannel. (Yay!)
Lossless is not really supported. Have you ever heard about SLS? Neither did I. To make it even more confusing, ALAC is also using m4a container.
It sucks at low bitrates. They tried to fix this not once (HE-AACv1), not twice (HE-AACv2) but three times (xHE-AAC).