HDMI cable made a difference in picture quality??


I just bought an a 42 inch LG LCD flat screen TV which is has full HD function. I have a HD cable box and opted to use RCA cables betwwen the box and TV. I am getting missed opinions from the cable provider and the LG dealer about the usefulness of the HDMI cable hookup. Does it actually improve picture quality??? If so,how much? and will it also improve non-HD programming??? I have seen several adds from Monster Cable and Audioquest touting their HDMI cables. Monster has one that is about $70; another is about $100. I have seen even higher price tags from Audioquest. All comments welcomed. Thanks Jim
sunnyjim
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"I actually A/Bed the $7.00 Firefold HDMI cable to a $100 Monster Cable HDMI and preferred the Firefold"

I'd better try the Firefold then. A $7 is better than a $100? Well, I agree price alone doesn't mean much sometimes. I am gonna order one and report back. If that beats my Kimber, I will sell the Kimber and get some Blue Ray discs. Thanks for the suggestion.
Yes, HDMI is better. Monoprice is the way to go. Difference in HDMI cables, only if they are defective, meaning they do not meet the HDMI spec. The IEEE rules on what the spec is. If the manufacturer brands his cable 'HDMI' they are claiming it meets spec. Recently the IEEE did a sampling of some cables and did find about 15% of those tested were defective, not meeting spec. So differences are often related to a defective product.
HDMI looks much better to me than component video. But, I have not been able to tell the difference between HDMI cables. The inexpensive ones I bought from Fry's look/sound as good as the Audioquest one the I bought to test.