I'll voice a different opinion I guess! I really enjoyed both Brussels and Bruges and feel that each deserve (at least) one full day. We were in Belgium for 4 days and went to Bruges for a full day trip and we never ran out of stuff to do in Brussels. there are lots of quirky museums (musical instruments, comic strips, etc). I did not find Brussels "grimy" but just a real, working, large city that had no more grime than say, Lisbon or Rome (both of which I also liked). Yes there are gypsies and the like, but I wasn't bothered by it. I also liked Bruges, so I think in the end either way you will be fine.They are very different. Bruges is a bit like Amsterdam with the canals and boat rides, there are some gorgeous little (and big) churches and the big squares are really beautiful - scenery-wise Bruges wins (except for the Grand Place which took my breath away each time). Bruges is clearly better for art, but Brussels has more in the way of different cultures and neighborhoods and things like that. They are both wonderful for chocolate ;) I love Rick's books but if you are reading his guidebook for Belgium, he gives a heavy weight to Bruges over Brussels - that's his opinion, but it's just his opinion, and I don't really agree.But perhaps most of all, and this is not even relevant to which city is better or more interesting, is that I don't even know if there's a difference between going from Bruges to Brussels in the evening of Day 2 or in the morning of day 3. staying there til morning won't give you more time in Bruges to sight-see, because it's not like there is a lot to do at night, but it would take useful morning time away from Brussels (or Bruges for that matter) in transport time, so why not at least give yourselves the full day there and go the night before, get settled, and have a full day in Brussels too? The train is only an hour, so going Day 2 evening after your full day should be a fair compromise and let you maximize both cities?