I visited Brussels and Leuven last week and found major differences in culture of the two cities. Netherlands is cleaner than Belgium but people pay higher taxes. Netherlands does not have Dubai type of multicultural crowd and the driving on the highway is quite sober.
Although Leuven is a small medieval european town and KU Leuven has a good international reputation, Leuven is quite small and laid back compared to Brussels with fewer amenities such as parks, etc. Therefore, if the choice is between living in Brussels and living in Amsterdam, Amsterdam is a better city than Brussels. Although life could be spartan in Amsterdam and the wine, food etc. could be cheaper in Brussels, nevertheless, Amsterdam looks more disciplined than Brussels. Finally the Dutch are descendants of Celts and the Belgians are descendants of the Germans. The Dutch are overwhelmingly Calvinists and Belgians are Catholic. That is why Leuven has great architecture and the Belgian women are more traditional than the Dutch women. It will be easier to date and find girlfriends to marry in Amsterdam than in Brussels. Amsterdam is closer to London and Brussels is closer to Paris and Berlin, spiritually.