I don't like to categorize by nationality, because in our experience, that hasn't been a metric which you can reliably determine whether a guest will be a "good one" or not. We get lots of different nationalities of guests, and there's "good" and "bad" in all of them.
The main metric that seems to reliably set expectations is families vs. groups of singles, particularly young ones. Families just seem to consistently lean toward the "responsible" and "conscientious" side of the spectrum.
Having said that, there are cultural things which lend to being rather "extraordinary" guests. And at the risk of doing precisely what I've said I don't like doing (above), we have noted that Germans/Austrians/Swiss in particular seem to be consistently clean, orderly, and respectful of the property. The same seems to apply to Scandinavian nationalities.
Now, we lived in Germany for decades, and could be rightfully accused of bias, but as @Anonymous and Ute surely know, Germans are stereotypically orderly, and are known for "Deutsche Sauberkeit" ("German Cleanliness"). Often obsessively (and sometimes, irritatingly) .
Generally speaking, in our case, that makes German guests more desirable. And we more actively market to German/Austrian/Swiss and Scandinavian markets for that reason.
Not that others aren't nice guests, but after German/Austrian/Swiss guests, we often find the villa looking as if nobody has even been there (with the exception of the beds having been slept in). Not always, but I'd say about 80% of the time, it's left pretty spotless. But it's also generally true with Scandinavians.
It's a cultural thing. Some other nationalities tend to be consistently messier, but nonetheless are also respectful and conscientious.
It's the groups of 20-somethings you need to watch out for 😳