If your goal is to maximize frequent flyer miles, then the AmEx Skymiles card is your best bet. Due to some things being always double miles (groceries, hardware, gas, usps), the random double miles on everything promotions, and the 10,000 bonus on renewal for 25K in yearly spend, your 30K in spend will likely turn into about 45K miles (assuming your spending is something like mine). You can also boost this through some additional manipulation (e.g. savings bonds during double miles promotions), but this is true of just about any card (perhaps not doubled). If you go for the Skymiles platinum you can also get a 15K signup bonus.

You may consider starpoints worth more (for free hotel stays) however, or be willing to give up some miles for the flexibility of choosing the airline to send your points to (all the biggies, except UA which has a 1:2 conversion rate). In which case Starwood is the better choice. The starwood card has a 10K signup bonus (search the starwood forum for a link) which gives you 4K for the first purchase and another 6K over your first 11 purchases at starwood properties (technically it is supposed to be stays, but any charge from a starwood property that is coded as lodging will get you the credit - some hotel restaurants will likely work).

All of the above assumes that your spend can be done primarily on AmEx which is not always a good assumption. In any case you will want a Visa/Amex to back up the AmEx for places that don't accept AmEx.

I agree with Human Unit that the Chase Freedom Card (formerly the Chase French card ) is a great choice. Unfortunately I respectfully disagree with most of the other things he says (the rebate is 6% for gas in the first 90 days the card is open, 3% afterwards, and 1% for all other purchases). The really great thing about this card is that the rebate is delivered as a card credit the next month as opposed to waiting for the end of the year. It also gives you the full rebate from the first dollar spent as opposed to other cards that only give you the full percentage after thousands of dollars of spend (e.g. discover).