When I had my wallet stolen in London about a decade ago, Amex was far faster, easier, and friendlier replacing my credit card than was Citibank. Did it at an in-person Amex office.

As an Australian, I’ve never seen Discover cards.

American Express has been largely replaced in Australia by Visa signature and Mastercard platinum cards that are more difficult for merchants to deny.

In Japan/Taiwan they seem to be widely accepted. Most places in Japan that accept VISA/MC, also accept AmEx.