CD vs FLAC stored on flash drive vs streaming

I was able to repair couple of unreadable CD by copying them to CD-R. It took long time (couple of hours for one CD) but got recovered working copies.

The opposite with me with original retail ones, the more they were burnt the worse the sound got.
Proved it many times when hearing a loved CD at a friends, borrowing, it to burn <4x, then later getting the retail one used same version and it sounds better 

But burnt ones that wouldn’t even read TOC were readable using another brand blanks.
The more they were burnt the worse the got, then there’s the burnt ones that are unplayable unless certain blanks were used, but perfectly fine with every retail cd.

It depends how you burn them.  Often people burn CD-Rs at 2x or 4x nor realizing, that laser is too strong at this these speeds.  I might be wrong, but I believe that at the beginning it was just physical burn of metalic layer.  Now, it is only high sensitivity photosensitive dye.  Every CD-R has training track for laser power adjustment, but it has limitations.  Photo dye, that can be written at 52x might be overburned at 2x or 4x, in spite of laser adjustments.   

It all depends on personal experience - I've used Taiyo Yuden CD-Rs with phthalocyanine dye with good results, but he best for me is memory storage - easy to use, good sound quality (with proper connection) and ability to create back-up copy (or multiple copies).

I've used Taiyo Yuden CD-Rs

They were all I ever used, but you have to watch out, because many being sold are fakes, then found other ones just as good.

Now I don't bother with copying just get the original retail uncompressed versions if any, and used if need be, as to me they are better.

If you with flash drives include hard drives my guess is that they sound the best. Less risk for error correction and timing problems. SSDs are really fast and proven to work. 

Drawback of SSD is limited number of write cycles. They increased it greatly, but at the same time introduced new architectures, like "quad cell" - where writing to one cell causes writing to four. It is not a big problem (nothing lasts forever) and no problem for music storage. It is perfect application for SSD (constant reading, very little writing).