That said, you need to experiment and determine which of the content supplied by your cable provider is in high definition, e.g. fits your HDTV screen properly, and what is not (and needs to be 'stretched' to a near fit).
It's not a question of 'best signal', but knowing which signal you are receiving and proper manipulation.
What is the best setting for a widescreen hd tv connected to Cox cable? At 16x9 The Weather Channel, for example, displays with black bars on the side. I can get rid of them by setting the tv to 4:3, wide mode, but I am still getting the best signal?