12AWG speaker wire

The Thicker the better. Between the two you listed I’d go with thicker strands but the cables will be stiffer 

The better the copper, the better the sound. Neotech UP-OCC from PartsConnexion. Make your own.

The better the copper, the better the sound.

Triple C will sound better than OCC which in turn will sound better than OFC and so on. Of course cable geometry, construction, solid core or multistrand, plus materials used for insulation and sheath play a sifnificant role also.

If making your own plenty to choose from big Japanese brands, Furutech, Nanotech, Neotech, Acoustic Revive, Oyaide (not order of preference).

@petg60 Triple C is not inexpensive! Furutech Alpha OCC DUCC DSS-4.1 is c.$500 per meter off the spool. Any other sources?

@rbull11 I found the solid core version superior to stranded.