If you want to argue KK vs DD, go
here,
There are plenty of both vendors in the Atlanta area, and as for coffee, I thin Starbucks is the best you'll find, there aren't any other specialized coffee shops.
As to Soul Food(tm), I believe there's a place on 14th street called the Country Kitchen that has good suthen food (thre are probably multiple places called the Country Kitchen in Georgia, but any would fill this niche) though I must warn you that, like The Varsity, grease and fat are probably important ingredients in everything they'd serve.