This question is from an argument I'm having with a friend of mine who thinks that 160 ABR sounds better than 192 CBR. I personally don't really notice a difference but I'd like to hear any opinions from the folks on this forum.

Neither. Use 192 ABR!

But really, the 192 CBR will likely sound better - maybe not enough to clearly ABX - but remember that it will be consuming 20% more bytes on average. So if you could be "prove" that 192 CBR sounds better than 160 ABR, then just use 192 ABR - same filesize as 192 CBR, but higher quality (due to VBR effect).

I encode mostly metal, and I can assure you that 192kbps CBR sounds better than 160kbps ABR. ABR isn't sufficiently better than CBR to be better at lower bitrates. It is, however, better at equal bitrates.