Card payment at Aldi (Süd) for me is about as fast as it takes Rewe to register that I put the card into the terminal. Aldi also never asks for signature and always goes for PIN because it's faster. It doesn't have to be slow, but sadly in most stores it is. (Debit card here, though. No idea how it is for credit cards and whether they work differently.)
If you ever have the chance to visit Sweden I urge you to try paying with card there (well, it's easier than cash there anyway). It's unbelievably fast.
But you are right, among the German stores Aldi has one of the best terminal.
