If you want to spend a romantic weekend in the city, I definitely recommend the Westin Peachtree Plaza. It's a landmark building, and with 73 stories, it's the tallest hotel in the Western Hemisphere. All rooms have a spectacular view of the city. Ask for a room above the 45th floor, facing Midtown or Centennial Olympic Park, as it's gorgeous, especially at nighttime!
When you arrive, if you have never been to Atlanta, take the elevator up to the 72nd floor and stroll around the viewing deck, or enjoy a drink in the rotating bar.
You get a very cool first impression of the city! By the way, they used to have life jazz up there on weekend nights. That was the greatest! If it's still there, it's great to start the evening with.