Depends on equipment, cable, and the rest in the chain, whichever sounds best. I have found that even 12awg are perfect for tubed preamps, CD players, power strips, but not for phono stages (tubed or ss).
What size power cable?
How “big” does a power cable need to be for upstream components? I get that amps can benefit from a large cable to carry plenty of current, e.g. 8-11 awg. Although my preamp and phono preamp have robust power supplies, they can’t possibly benefit from such capacity, can they? Extreme overkill is the norm in hi end, but is there any benefit to more than 12 or 14 awg on a preamp or phono preamp? Much less digital components.