Common wisdom is that shorter is better (for USB cables, at least).
My experience is quite opposite. I have directly compared, at length, in my system, 1m against 2m:
- Supra cable: the 2m one had stronger and more authoritative bass, more drive, perhaps more highs; the 1m brought the mids more forward, the mids were more colorful, more enticing and the highs might have been slightly more refined. Overall I preferred the 2m one but I could imagine systems and ears for which the 1m one would be better
- Curious cable: the 2m one was clearly better on all fronts, no contest. The main advantage was, again, bass and the impression of a more dynamic sound