I've done both the Epcot and the GA Aquarium dives. The GA dive is much more expensive but the tank is huge and you'll see considerably more species of fish, sharks, rays, etc. The sea life in the GA Aquarium looks like it is in pretty good shape while the tropical fish in the Epcot tank look a little beat up in comparison. Both programs have a behind the scenes tour which is pretty interesting in both cases. Both dives are worth doing as 'bucket list' type dives: fun to do once or twice, but given the expense, not something I'd repeat very often unless I got some sort of major discount. So if you'll be in Atlanta, definitely do the aquarium dive: its fun. If you're at Disney and the crowds in the park start driving you crazy, do the Epcot dive too. (BTW: you don't have to pay the park admission fee to do the Disney dive: if you don't want to go to the park, the Dive Master will meet you at the customer service area outside the park).
If one were visiting Orlando, note that Jupiter is only a little over 2 hours away and has some world class drift diving where you're likely to see sharks, goliath grouper, sea turtles in their natural habitat.