We did Atlanta over Spring Break and we used the CitiPass. In my opinion if you are interested in the attractions that are offered it is a great deal. I purchased it online and printed my receipt then picked up our booklets at the first attraction.
We did the Zoo, CNN, Coca-Cola, Aquarium, Fernbank Museum, and High Museum of Art (they had the Terra Cotta Warriors Exhibit from China when we were there). We also did the Olympic Park (free). We did all of this in two days.
Check online for the Aquarium website for current hours and specials. We went right at opening one morning and did most of it before the crowd got heavy. Don't miss the Beluga Whales!!
You can park at the Aquarium and walk to Coca-Cola, then walk through Olympic Park to CNN. Great food court in the CNN building for lunch.