Vladimir said:
By default thicker is better in all cable applications, including USB.
What's more important is to have pure copper, not CCA (copper clad aluminium). A smaller gauge pure copper wire will outperform a thicker CCA one.
While I normally agree with Vlad, there is nothing intrinsically wrong with CCA. Sure, if you have two cables the same thickness, then copper wins over aluminium. Use a thicker aluminium cable.
Equally if you have two cables the same weight, then aluminium wins over copper. Where weight really matters (overhead grid cables for example) aluminium cables with a steel core for strength are used.