I did all 3 cities this past December. I tend to tour quickly, so I took 24 hours for Brussels, then took the train to Gent (spent about 2 hours there), and then trained to Brugge. Brugge is very nice, albeit touristy, but in that fairy-tale way. Stayed at a very nice Relaix & Chateau hotel about 10 minute walk from the town square.