Is, according to a story in Slate, Aldi's. Do you know these facts about Aldi's?
The grocery chain was started in Germany by two brothers, Karl and Theo Albrecht. In 1960 they had a falling out over something and separated the holdings geographically. Theo took northern Germany and his stores were called, Aldi Nord. Karl got the southern portion and his holdings were named, Aldi Sud. The became two distinct companies but similar.
Both the Nord and Sud Aldi's came to America, Aldi Sud does business as Aldi's and Aldi Nord does business as Trader Joes.
Trader Joes! Yes this chain also Aldi's.
But why Slate considers Aldi's the best grocery store in America seems to be that shoppers are made to bag their own groceries which accounts for lower prices.