Actually, HDMI is almost certainly better. HDMI gives an uncompressed digital signal. Digital broadcasts, whether ATSC over the air or QAM from cable, are always compressed. To give a couple numbers to this, an uncompressed 1080p video stream (with chroma subsampling, not counting audio) takes over 700 Mbps, but QAM transports up to 38 Mbps (including audio). In contrast, HDMI transports over 5,000 Mbps. QAM encoders are getting cheaper, but I think NTSC is way cheaper and more suitable. TVs without HDMI aren't likely to have QAM, anyway, so the cable provider will use NTSC.
I doubt that you really need to get those overpriced HDMI cables. Deals web sites are always publishing HDMI cable deals, like 3 6-foot cables for $10 or whatever. I don't have the patience, so I get cheaper cables from monoprice.com.