Good credit limit and good customer service.
I have 4 cards, Chase, Visa, Captial One, and this Amex card. Of the 4, American Express gave me the highest credit limit by far, almost double my next highest card which is nice if you are someone that likes to be able to actually use a card and keep your card use under 10% to keep your credit score healthy. I use all my cards but when I am making an online purchase with a new or unfamilure vendor or company, or a site where there is a chance to get ripped off etc, I always go to my American Express card because I know if there is any problem with the purchase Amex will quickly help me fix the issue. They have been very good at helping me to stop payments to a company that was charging me recurring payments that could not be canceled any other way, it is also easy to file a claim and get your money back if you get charged for something you did not get delivered and the seller refuses to give a refund or replacement. Any payments that have the potential to have some kind of issue like that I go to my American express card because I know they will have my back.