Hmm, HTML of course, that could be limitating to non-HTML knowing/daring collegues. I must admit that I make my exercise off-line (in HTML), because it's easyer to create a lot of similar but yet different exercices (cut, paste, save, cut, paste, save...). Anyway, the assignement-module is also with the HTML-editor. The two possibilities would be nice 
Now that I've created and assessed an exercise with real-live students, I'm going to review the dutch translation too. It's easyer knowing what you're writing about 