Aldi is more like a small-scale Costco - a sort of ‘warehouse’. Lidl is different - it’s like a neighborhood grocery, and not so big that it’s difficult to navigate for us older folks. In our experience, you can also find the same things routinely at Lidl. Our experience with Aldi is like Costco - sometimes they have something, sometimes they don’t.
We like Aldi, especially at Christmas time - they have lots of nice European holiday treats - and we got one of our best Thanksgiving turkeys there, for a very good price. But in our area, the store is so crowded on weekends and parking is horrible. The nearby Lidl is very convenient, and very friendly, and the stock is organized like a regular small grocery.
Lidl, Aldi and Trader Joes are all German grocery chains. The Germans seem to have cracked the grocery formula like no other grocery stores in the world.
I’ll be sure to look them up! :)