I have upgraded from a substandard set of unbalanced RCA's (what you might find out of the box of a DVD player) to a slightly better Monster Cable M350i interconnect. I didn't know any better at the time of purchase: I thought there was only Monster Cable as a performance option. I will soon be upgrading to Analysis Plus, perhaps their Solo Crystal Oval's.
I have better experience with speaker cables, as far as differences noticed in listening, but the Monsters did offer a bit of change. I have noticed a tremendous difference with Analysis Plus speaker cables, especially over the Monsters, so I am hoping the same applies with interconnects. I do have an Analysis Plus optical cable, which is much more revealing than my former Monster Cable M1000, a surprise given the digital nature of an optical interconnect.
I had some AlphaCore Goertz silver RCA interconnects for some 300B monoblocks that I liked. I then got some new, significantly different amps (hybrid monoblocks with significant more power) and they sounded horrible with these new amps. With the new amps I was able to swith to balanced interconnects and went with the Nordst cable line. I am very happy with the Nordst line. I had a hodge podge of interconnects, speaker cables, and power cords in my system. I'm now 100% Nordst and am very happy with it.