Choose Dutch unless there is a real reason to use English.
English often feels international and cool, but it lacks the precision and tone of your own language. A Dutch slogan fits a Dutch-speaking team, a Dutch-speaking audience and the way people talk about the event.
English makes sense when your audience is international or when your brand deliberately operates worldwide. It can also help if an English phrasing hits a nuance that does not work in Dutch.
In doubt? Write the Dutch version first. If it works, you don't need to translate. If it doesn't work, English won't save it either.