I don't know if it's supposed to perform higher quality but I've seen multiple tutorials saying to NOT USE AAC+2. Just use AAC cause I've had great results with it. I would say to put the quality to 48.000 khz 8 bit cause once again I've had no problems with it. Here's a video I did with 48.000 khz 8-bit(If you don't like the sound quality then you can try 16 or 32 bit.):
Real simple answer. Always make your masters in high quality. There is no reason in this world to render out something with less than 48k 16bit audio in a master. Any compression that follows is a different story. But just because it will end up 8 bit once compressed, why start degrading your audio before compression degrades it again.
I recommend not going any lower than 16-bits. 16-bit/48kHz seems to be the standard for video-based audio and you'll end up compromising the quality of high dynamic range material with 8-bits; with music music 8-bits isn't terribly noticeable because it's mixed to remain fairly loud.