Hilton’s third quarter promotion, which runs from July 7 through September 30, offers HHonors members either double points or double miles for all stays. Once you choose whether to earn points or miles, you can’t change your selection.
In general you’re better off going with double points, as you earn an additional ten points per dollar spent. As Loyalty Traveler points out, a Diamond member using the American Express Surpass card earns 39 points per dollar. So for about $1,250 in hotel spend you’d get 50,000 points, enough for a category 7 hotel.
On the miles front, you’d be best off with bmi. Through bmi you normally earn 1,000 miles per night, with a maximum of 3,000 miles per stay. Through this promotion you’d earn 2,000 miles per night, which is quite nice.