Thanks, I did mean Groningen; the difficult access is part of the appeal really. I'm not a huge fan of Amsterdam: even without the stags it's pretty crowded and intense. But there's no denying it's handy access to the continent. I was working on the assumption G is quieter?
I enjoy a bit of Euro train travel: accessibility to Germany and lots of Hanseatic architecture is also part of the appeal.
Never been to Rotterdam, but it's on the way to Belgium which, for my money, has some of the most underrated cities in Europe. Might give it, or Scheveningen a look.