lol, I did audio hearing test (not blind one, but trying to hear differences intentionally as hard as I could) and here's what I got for mp3:
up to 128kbps, easilly detectable. I perceive so much losses, it's not worth to review.
192 kbps: somehow detectable, but I still don't give that much respect with the losses.
256kbps: quite hard to detect and I may not detect it on blind test, but remember that if I really love a vgm, I could listen to it for months and even years for a crazy amount of loops that it could become apparent.
320kbps: honestly, if I have to use it, acceptable because it was really hard, but I did spoted a tiny difference. The problem is again, I'm VERY picky so in long term, it's safe to go for better quality since music that got engraved in my head like ssbm menu 1 can become a bit easier to spot differences.
I didn't tested AAC, but I know it's a bit better than mp3.
Lossless is good if it's not on high compression. For flac, my converter had low, normal and high compression. I did noticed a difference on low, but at normal, I tried as hard as I could and I noticed nothing. For safety, I could use low compression and be fine for a very long term usage.
So, that's why I wonder what bitrate and codec youtube uses.
But I may switch to low compressed lossless after those tests. I really tried and it may be good to use flac instead of wav.
Btw, itune uses lossless and the quality is very good.