Pros
The benefits and wide variety of opportunities (both locational and positional) are the best reason to work at American Express. If you are a minority you also have a strong advantage. Approximately 60% of management is women. You are 4x as likely to be in management as a woman than as a man. They also provide childcare and other related benefits. 3 weeks of vacation are standard plus the option to purchase an additional week. They also offer excellent healthcare, legal assistance, babysitting assistance, tuition assistance, etc. It is a company that also gives back to the community and allows opportunities for service.
Cons
Similar to any other company it is often "who" you know and not "what" you know. There is a lot of movement within American Express and you will quickly find that the best way to get ahead is rarely with a promotion, but more often through internal movement. They are a fairly large company and in this way it is difficult to be recognized. They also tend to have tons of Directors and VP's in New York that are at Manager level outside New York. Often the only way to get a higher salary is to accept a position in NY at headquarters and then transfer to another city taking that higher salary level with you.