In other words, both are correct. Choosing the one that's appropriate in a specific context...is a tricky problem.
> because it looks very ugly when you only drive through it on the highway
A lot of places look ugly if you stay on the highway.
Your attitude pegs you as a fellow Dutchman holding the classic but outdated, tiresome, and condescending view of that city that you only pass it on your way to France for the holidays. But do stop there some time, the past decade has been kind to it (the modern train station is beautiful). Keep in mind that this is a large city in an area dominated by the coal industry for the better part of the twentieth century.
What I find interesting is that the road signs in the Netherlands say Liège whereas in the few km of Vlaanderen on the way there, they insist on Luik. But this is what makes Belgium, Belgium.
/rant