Amex rocks. (I’ll relate my experience with the Platinum Small Business and personal Gold cards…also, don’t think these cards are special or hard to get, hell, they gave them to me!)
The best thing is their customer service. Their phone support simply blows away any other experience I’ve had with other cards or banks. You also get a total spending summary at the end of the year, organized by category (nice for taxes). They were also the first card to offer insurance coverage to car rentals (just decline the rental company’s.
Keep in mind the traditional Amex cards are charge cards, you’re supposed to pay them in full each month (though they do offer finacing/extended pay on the biz cards.
If you pay quarterly taxes, you can also pay with your Amex and get tons of points (assuming you’ve signed up to one of their point programs)
Overall, the Amex card is great if you expense a lot for your work and get reimbursed—you just loop everything through the card to get points.
(btw, I would look very carefully at the other, newer products they offer—like the clear/blue card. Word from an Amex employee is that they are not a good value)