Both are fine cities. Follow the links Marc provided. The Royal Museum in Brussels is great. The 2 museums in Liege are worth the trip. Just across the street from Liege is Herstal where FN is still located.
People are very friendly in Belgium. There are 3 official languages, German, Dutch and French. English will be fine in either city. Brussels is home to the EU. Liege has become a university town during the day. If you can be in Liege on a Sunday, there is a huge market along the river that runs for miles.
Belgian chocolate is to die for!!! There are over 1,000 artisan beers available.
Pete
