Quality cables are shielded better, use better wire, and/or are routed better (twisted and all that as needed) so there is less interference from outside sources and less signal loss due to distance. Additionally, DVI cables usually give a better image than VGA cables (of the same quality). I'd probably pick a high quality VGA cable over a low quality DVI cable however.
Mike.
<font color=blue>Outside of a dog, a book is man's best friend. Inside the dog its too dark to read.
-- Groucho Marx</font color=blue>