I was never a fan of AMEX since they charge businesses so much, and thus aren't widely accepted. However,if you are looking to add a new line of credit, the American Express Blue Cash Everyday card could be a great choice.
Why I have it
It's not the most versatile card, but it is the only card that gives 3% cash back on US Supermarkets with no annual fee. The 2% and 1% cash back on other categories are useless to me since my Barclaycard gives 2.2% on everything. But everyone shops at supermarkets, and since this card is free, it's a good one to pick up, if not just for the $50 promo bonus, free year of Amazon Prime, and 15 months of 0% APR.
The Blue Cash Preferred Card is not worth the $75 annual fee, other than that, there's not much else to say.