Hands down best card for all around usage and cash reward- Citi Double Cash, 2% cash back on everything, with no categories and no limits-amazing, keeps it simple! It is a MasterCard, so in order to have an AMEX, I would also recommend the Hilton HHonors AMEX. Unlike any Marriott card, this card always gives you HHonors Gold level at any Hilton property, which can be a big plus--lounge access and some type of free breakfast at all properties. It has good points rewards also, especially on gas (12 points per dollar.)
If you are a Costco shopper, I would also recommend the (upcoming on June 20th) Citi Costco Visa, 4% back on gas and 2% at Costco, 1% everywhere else.