The Amex Plat card offers benefits for all 3 companies - are most of you renters members of all 3 or are loyal to 1 only? I'd like to hear what you choose and your reasons. In your experience, do you get access to all the written benefits? Upgrades, discounted rates, shorter lines, etc. I am particularly interested in JFK/LGA/EWR, IAD/DCA, PHL, ATL and MCO. Thanks.