I second Tony Caputo's. Phenomenal sandwiches.Density, probably not. But that doesn't mean that chains are best they have on offer.
Backcountry Deli is a small Colorado franchise that makes some pretty mean subs.
Tony Caputo's .. Italian deli in Salt Lake City, complete with locally cured meats and nice sub menu.
Go to pretty much any other city or sizable town across the country, and I'll bet you can find something better than the chains.