I had clients stay at both in the Fall, and both were a success. To me it is more about the location. If you haven't been to Brussels before, or want to really explore the city, then I would go with Amigo. It's right in the heart of the city and very walkable everywhere. If you have to been before or don't really plan to explore much, then I would go with Corinthia. It's newer and fresher, the staff is great, and it's not right in the craze but still just a ~15 minute walk to the city center. Corinthia is much more of a "grand" feel to it whereas Amigo is still large but feels more intimate.