Starwood American Express 25,000 Point Sign-Up Bonus
Update: Some offers mentioned below are no longer available. View the current offers here - Starwood Preferred Guest® Credit Card from American Express, Starwood Preferred Guest® Business Credit Card from American Express
While I think the Hyatt card is a better deal (the equivalent of 60,000 Starwood points if you use the two Hyatt nights at top tier hotels) because they don't require any spend to get the bonus, the Starwood card does offer incredible flexibility because of their generous airline transfer ratios. For example, 20,000 Starwood points transfers into 25,000 airline miles with a lot of airlines. 20,000 Hyatt points will get you 8,000 airline miles. However, Hyatt's nicest hotels only cost 22,000 points vs Starwood's 30,000.
The great thing is, as long as you have good credit, there's no reason to not get a Starwood and a Hyatt card. They are issued by two different lenders, so there's no conflict in getting both.