Antwerp/Ghent in a Day?

Personal opinion question, but I preferred Ghent to Antwerp and both over Brussels. If I was going to stay in one rather than return to Brussels, I’d choose Ghent since it’s between Bruges and Antwerp. In all fairness, we stayed two nights in each and enjoyed both.

I'm laughing that I'm chiming in here, because I haven't ever been (lol) but Belgium is VERY high on my list and I've spent a lot of time reading the Belgium forum. What I've learned is that unless you have a particular reason for prioritizing Brussels, most people find it underwhelming, or deserving of a half day max, and far prefer time spent in Bruges, Ghent, and/or Antwerp. Ghent is less picturesque than Bruges but has a more lived-in feel (more students and locals, fewer tourists), and Antwerp gets a lot of love from people here. It's a big city and could easily fill multiple days, but a friend of mine had two nights there and still fell in love. (She also stayed a few nights in Bruges and did a daytrip from there to Ghent.)

Only you can answer your question correctly, as we have no idea what your interests are or which spots you'd like to visit in each city. Even the date you plan this visit can have an impact depending on whether some important event is taking place.
Let me also mention that reaching Ypres (by public transport) is easier and more practical from Ghent than from Bruges.

I can understand the preference for cute, smaller cities over Brussels purely for walking around; the Grand Place in Brussels is beautiful but tourist-swamped. However, I would be remiss if I didn't report that I willingly spent 13 nights in Brussels earlier this year. It is rich in Art Nouveau architecture, which I love, and has some good museums, despite the current closure of two parts of the Royal Art Museums.

I haven't gotten to Antwerp yet, so I don't have an informed opinion about it. However, I wouldn't choose to split a day, or even 1-1/2 days, between Ghent and Antwerp.

I too love Brussels. The problem with Brussels is that it takes longer to give up its charms. If you are just the casual tourist, there for half a day, you see only the Grand' Place (which is stunning by the way), the peeing boy and all the tourist crowds. But if you give it a bit longer - say 3 - 4 days - then you have time for the museums, the architecture; the 44 tram from Montgomery to Tervuren is Brussels' prettiest tram ride and you can visit the Park de Tervuren and the Museum of Central Africa at the end of it. Brussels is also a lifestyle city and by that I mean food is very important. Take the time to go to some of the better restaurants like those in the Galeries Royales de St.-Hubert or tarry a while in the bars of the Parvis de St. Gilles or Place du Luxembourg. I also like markets and Brussels has many of those; the Saturday antiques market in the Sablon is just lovely. Stay somewhere nice like Le Dixseptième on in the Sablon. Go shopping in the Louise district. Cocktails on the rooftop of The Hotel, which has a view. Brussels has its kinder side, you just have to look for it.

Lavandula

Antwerp also has a respectable amount of Art Nouveau and Art Deco architecture. It is smaller than Brussels but far larger than the other named cities. It also has a large number of diverse museums, including the world class KMSKA, home to dozens of important Rubens paintings.