YS offers the better meal and experience by far. It's one of the best restaurants in WDW - quiet, sober, formal - even if it's somewhat overpriced.
Concourse Steakhouse, on the other hand, is a mediocre steakhouse, of the kind you'll find in your town or city back home. It's good for a no-fuss breakfast (try the Sticky Mickeys) or lunch, but not much more.