Solid core OFC vs stranded OCC copper

I personally prefer to sonic signature of solid core OCC copper.

for what application?

Stranded copper because it is far more flexible. IMO there is NO sonic difference between stranded and solid core.

I use solid core for internal chassis wiring and stranded for everything outside the chassis.  I do a lot of DIY stuff, so that makes sense to me.

I'm same as spatialking. using stranded for internal can be issue with extremely small gauge wiring, frying individual strands when soldering. As for SQ, no overarching reason for one over the other IME.