Brussles or Ghent??

Why not do both? Brussels is only an hour from Bruges; Ghent is a half hour. You could conceivably see both in a single day trip. Brussels is much bigger of course and deserves more time, but you could pick a couple sights such as the Grand Place to see in a half day. The trains between those three cities are very frequent, so transport will not be a problem at all.

Gent is similar to Brugge, but because it hosts a large student population and it never experienced a sharp decline like Brugge, it's a much more lively city. Unlike Brugge, where the charm hits you almost as soon as you leave the train station, you have to make your way through several blocks of a fairly ordinary modern city until you reach the historic core. Personally, I'm a much bigger fan of Ghent. I loved Brugge the first time I was there, but it gets less interesting each time. Brussels is sort of the opposite of Brugge. It gets better the more you explore it, but it isn't nearly as immediately pretty. The interesting sections of the city are also fairly geographically dispersed and separated by rather ugly blocks of modern concrete. With a little effort, the city really opens up. There is a pretty good collection of museums. Don't miss the Musical Instrument Museum, and if you have even a passing interest in the world wars, the Royal Museum of Military History has a huge collection of material from both conflicts. The city also has some very attractive urban parks, and a great sampling of architecture (minus some of the atrocities committed from the 1960s to 1980s).

No, I don't think that Gent is like either Brugge or Brussel. They are different. "what is better"? Who knows - I know not what you or your parents want from a Belgian city. Gent is a living city, with a large university, a big hospital, many hotels, lots of good restaurants, few B&Bs, the reconstruction of the tram system is complete, the town is wonderful, an Adoration of the Magi, and the best chocolate for my wife and me by far is in Gent. Brugge has a much, much higher ratio of tourists to residents, more B&Bs, fewer hotels, a good art museum, neat church over church, many horses, lots of dodgy (highly touristed and not good quality) restaurants, lots of tourists, great architecture. Brussel is a big city, the capitol of a country without a functioning central government, with all the gritty stuff of a big city. There is a nice central square but I found the rest of the city difficult, with mostly narrow pedestrian sidewalks, plenty of graffiti, and the museums and attractions are spread out around the city. There are tons of business class multi-starred hotels scattered around, some of which have excellent deals on summer weekends, I have never heard of a decent B&B there. I think it says something about a city if its claim to fame is a short (yes, really short) statue of a boy with a toilet problem (yes, there's one of a girl in a similar fix a few blocks away). We visit Brussel, usually as a day trip or staying overnight while changing trains, or as a staging area for our last day before driving back to the UK (BTW- you have to experience Belgian driving, as I did again day before yesterday). Given a choice we plump for Gent. We like Brugge a lot, especially out of season. We put up with Brussel. YMMV.

Nigel said it far better than I could. I've been to Brussels more than anywhere else in Europe due to a previous employer. I can't imagine ever going back on purpose. The Grand Place is worth walking around and having a drink at a cafe in the square. You can wander the streets around the square and see the Manneken Pis. I haven't had the honor of seeing the female version. Brussels is worth about half a day IMHO. I can see it as a stop over on a train trip but I'd rather just switch trains. I've not been to Gent. Bruges is an interesting city but not worth more than a day. Head over to Haarlem or Amsterdam.

"I haven't had the honor of seeing the female version." That would be Janneke Pis. She deserves far more attention than she gets. She's got this funny little facial expression that seems to say "I know I shouldn't be peeing here but I'm doing it anyway."

Have you thought about Antwerp at all? I thought it was a great city to visit. I am one of those people who sort of likes Bruges, but it gets on my nerves as the sheer amount of tourists tend to detract from the enjoyment. It is cute and quaint, but I can't imagine spending more than one day there. Big cities are more my taste as they are interesting and if you give Brussels more than a superficial visit, you may find a lot of things to like there. Architecture is a high point as well as the museums. Strolling around some of the beautiful residential neighborhoods is a treat. Visiting antique stores, or stopping by a street fest celebrating the muli-cultural aspects of the city were the highlights for me the last time I was there.

Tom has given you very good advise; there is much to see in Brussels, far more that Bruges and Ghent put together. It is easily worth 2 to 3 days, partially because things are a bit more spread. One can easily see Ghent in a couple of hours. There are about 10 blocks of interest. And, yes, Bruges is spectacular, but while I have been there only once, I can see where it would get old fast. About the only similarity between Bruges and Ghent is that Ghent also has a canal.