As a Monster Cable® guru, it depends and your funds, and how selective your listening is.
The video cables have the most impact, especially with the 1080I TV's. I am using the M-Series Line, and feel they merit some looking into. As for speaker cables, the Z2-Reference are beautiful, however the black box they are packaged in, is a nonvalue added prop.
As for the audio cables and speaker wires, buy as good as you can afford, without overdoing it. (Put your money in a nice pair of Klipsch RF-7's) Spend your money in your front (main) speakers, and stay with the medium line of cables at Monster.
Good Luck with your purchase!