I get "free" access to both, and though the Centurion lounge has a significantly better selection of food and beverages, it can also be incredibly crowded, with children left to run amok as their parents relax, etc. I'd say this is true of MIA and other locations with Admirals Club and AMEX Centurion Club lounges.

I'd save my fifty bucks, frankly; that's a lot for what IMO is essentially a nice college duning commons breakfast.