Even without the Centurion locations, the lounge access provided by American Express is vastly superior to Capital One, Chase or Citi. Make sure that Priority Pass is a good match for your travel pattern.
Capital One only has 3 lounges, Dallas, Dulles, and Denver. PriorityPass is a joke within the US. Amex gives you access to Escape + Centurion + SkyClubs when flying delta. Centurion members have reserved space at Centurion lounges, as well, correct?