Putting aside whether the points & benefits value are the best in the business anymore (I think they all got a lot worse post ZIRP)..
Amex gets the majority of my spend because they are cardholder friendly and easy to deal with. I never spend time in opaque phone trees, waiting for callbacks, on hold or having to argue/escalate any issue.
Their website is good, their phone support is good, and I feel protected using the card vs having to deal with some random issuer of a branded Visa / big dumb bank / etc.