what's the most vital cable in a system?

I was wondering what IS the most important cable in a system if one was to rank them (#1 being the most important and so on)...A local dealer said that to him, a digital cable is the most important cable if your system calls for it....Well, my set up is a Classe CAP80 integrated, Epos ES14 on dedicated stands, a Toshiba SD1200 DVD/CD player, an MSB Link III DAC, and a Monarchy DIP jitter box. I use 2 digital cables with this set up - Canare digiflex and a Monster Video 2. I am thinking of upgrading the Monster digital cable...As for the rest of my cables, I'm using a Synergistic Research Mark II interconnect and Audioquest Indigo + speaker cables?...comments???