The euro counterfeit business seems to be rather adaptable. Now that 100 and 200 € notes are looked at with suspicion by most merchants for a long time and the 50€ note has become (rightly so) also kind of suspect, the move seems to be into the 20€ and a bit into the 10€ note. While the 50€ seems to be still the sweet spot due to its good balance between high volumes in circulation which minimizes the scrutiny that a merchant spends on one note, the 20€ is clearly up and coming. So watch out for counterfeit 20€ notes. Also notable is that the 500€ note (I can not remember to ever have seen one in the wild) seems to gain popularity. If you do the math, it makes sense. If you can make a good 100€ or 200€ note, the step to 500€ is not that large in terms of production cost. But the gained net value is five times or 2.5 times as high. Still no reliable data on planned introduction of RFID tags into the money, which will open new opportunities to counterfeiters.

Data Source: ECB

PS: the total value of confiscated counterfeit euro notes is still at the peanuts-level: 15.229.500 €