I think it depends on the store. There are two stores within 3 miles of my house. One of them offers a dozen eggs for less than $0.50. The other offers the same eggs, from the same supplier for approximately 2x that amount, which is competitive with Wal*Mart.
So it's hard to make a blanket statement as each store seems to have some autonomy on how they will price items.
Both are convenient to me, and I keep my eye on those staple items and stock up (with in reasonable limits) when one is offering a deal over other options. I can use a dozen eggs in no time, so getting 2 or 3 dozen makes sense when they are sub $0.50 per.
Originally Posted by NO2
Aldi is not cheaper for loss leader items, like eggs, bread and milk. They are a lot cheaper for things we buy a lot of, usually 10-30%. Things like Artisan lettuce, mini carrots, ketchup, hummus, apples, onions, and produce items in general. They are even cheaper for sugar, flour, spices, and other baking goods. And getting out is a lot faster than Kroger, Meijer, etc.