Had snob mussels at both recently. Bier Market on Esplanade wins although both were good. However, as expected, Cafe Brussels is the better dining experience. One should only compare the food as Cafe Brussels is a full-time restaurant whereas Bier Markt is bar with a decent dining area.
Cafe Brussel: great decor; great wait staff; good wine selection although limited at lower price range; highly recommended.
Bier Markt: been many times; balanced bar and dining area; great beer selection (fair priced); food prices are tad high (eg $9-11 for desserts!); service has historically been spotty although it was good on Jan 2 visit.