Amex is great. I have only once found a place that doesn't accept it.
I find they will do more for me than companies like Visa, they have many different services.
I have booked flights on Amex and got them to change the seat when the airline themselves said 'sorry, it's too late to change'.
Best time was when I was in Vegas. Amex has relationships with many popular restaurants and clubs where they get good treatment, faster bookings, etc.
I couldn't get into a club where work colleagues were becuase it was full ('capacity' they say in the US). There was a long queue and people were not coming out. It was looking like many hours wait.
Called Amex, told them I wanted to spend the evening at said club and I wanted to get in, they confirmed they had a relationship with them, or it was on their list, whatever. Gave it 30 minutes, went back right up to the front and found that we had been put on the guest list. Didn't even have to pay the $20-30 to get in.