Remember, when thinking about digital cables, such as HDMI, a better cable doesn't make the 1s any straighter or the 0s any rounder :-)
Digital only works because there is a range of voltages that are all 0s and a range of voltage that are all 1s. You are in the non-linear region. So, even if someone claims that voltages will be more accurate with a particular cable (which they probably aren't), it doesn't matter since it is a digital signal.
The one thing to remember with HDMI is only buy High Speed. Also remember that there is an HDMI section of the AVSForum where this question has been asked many times.
Also remember next time you are in Best Buy, how much pure profit they made off of you with those cables.