I opted for the AmEx Platinum card for the Centurion Lounge and Priority Pass benefits, plus the $200 airline fees and TSA Pre-Check.
I typically fly from my home port of SJU to SEA through MIA. SJU now only has a Priority Pass lounge, which is decent, particularly for delays. MIA has a full Centurion Lounge in the D Terminal, so it's convenient for my AA flights and I can bring in up to two guests for free - but it can get crowded. (Benefits include free mini manicures and massages.)
SEA has a smaller Centurion Lounge, which I actually like over some of the others, but you are limited to one free guest because it's a smaller lounge. It serves regional beverages, like beers and local sodas. The staff seem more attentive in the smaller location
I've also used the Centurion Lounges in LAS and DWF.
Last weekend I was pleasantly surprised to find a Priority Pass lounge in UVF (St. Lucia) after I learned of a 5 hour mechanical delay - it was a much more enjoyable place to spend the time awaiting the flight, and I brought in one guest for $27 - totally worth it given the long delay. This one wasn't a high end lounge, but it was clean and comfortable with a bartender and light snacks. We were able to bring in food from the food court, which was better than the snacks. The WiFi was abysmal.
Access policy: Centurion® Members and Platinum Card® Members who receive complimentary access may enter with either up to two guests or immediate family (spouse or domestic partner, and children under 18) at no additional charge. Guest or family access is per Card Member, not per Card. Family and guests may not enter or remain in the lounge unless accompanied in the lounge by the Card Member.
I use an app called Lounge Buddy that tells me what lounges are available within each terminal and the requirements for access - AmEx, Priority Pass, class of service, etc. Priority Pass also has an app.