I do not have direct experience with USB cables (I only made one for myself, but don't have good USB transport). However, all other testing for both digital cables (S/PDIF and AES/EBU) as well as analog cables all show that high grade solid-core conductors are superior. In the case of digital cables, silver does actually improve things.
The two/three cables I would probably consider are:
Nordost Tyr 2 USB ($1600 for 2 meter) 20awg conductors.
Nordost Valhalla 2 (probably $4.5k for 2 meter) 20awg conductors.
Oyaide Continential 5S ($495 for 1.8 meter) 24awg conductors
The Nordost cables get seriously expensive. My experience with Nordost Heimdall 2 Digital COAX is that it has a lot of depth in the sound, but it's somewhat laid back in the upper mids/highs.
The Oyaide is solid-core pure silver 24awg conductor, which could be very good.
If anyone has direct experience with these, please post.