Bruges or Brussels as our base?

I have been to all four cities several times and. agree with the input you’ve received from your friends to base in Bruges/Brugge. It is a beautiful city with most of its historical medieval architecture intact, has great museums, is only 25 train minutes from Ghent and a little more than an hour by train from Brussels. It is simply more pleasant.
There’s a reason more than half of all visitors to Belgium go to Bruges.

I would stay in Bruges over Brussels and Ghent over Bruges because of all the tour groups clogging up the sidewalks. I have stayed in all 3 cities.

“ Ghent seems to be perfectly situated geographically, but it doesn't sound interesting enough to make a home base.”
Ghent would be the ideal base for your itinerary plus it is a great city in its own right. Ghent has a nice historical city center complete with medieval castle right in the center. It also has beautiful churches, nice museums and great restaurants and cafes. On top of that it isn’t completely overrun by (cruise) tourists like Bruges. Bruges may have the name and fame, but Ghent is a much nicer city in my opinion.

Bruges! Always Bruges! The most beautiful, peaceful city in northern Europe.

No contest; BRUGES!
We found plenty to sightsee there, and you can easily day-trip to Ghent and Antwerp.

We didn't have a lot of time in Brussels but first impression didn't trip our trigger.

Everyone will give you a different answer. I'm one of the Antwerp fans, especially for multiple days. That is, depending on museum closing days, you can see most of Bruges in a day. That's not true of Antwerp or Brussels. But I don't prefer to sleep in Brussels. You might consider access to the train station in evaluating your Bruges housing choices. Is it air-conditioned?

There is no doubt you will enjoy Bruges. But it you make the mistake of believing that it is a superior experience (occasional canal odors aside) to every other city in this part of Belgium, you won't start on your daytrips early enough.

https://community.ricksteves.com/travel-forum/belgium/day-trips-from-brussels-768c7c85-75b9-4374-ad13-ae36967bc521

In her opinion, Bruges has more to offer in terms of history, culture and art.

Of course she is entitled to her opinion. I believe that statement is wrong. If you define the quality of art by being included in The Monuments Men or a single piece by Michelangelo, you can vote for Bruges. But for quantity and quality, you can't overstate the value the Royal Museums of Fine Art (and other museums) in Brussels, and the (reopening after many years of renovation in September, so not available to the OP) stunning KMSKA in Antwerp, Bruges is a one-day wonder. Sure, there are few rare, early paintings in Bruges. How about 50 major Peter Paul Rubens on view every day at KMSKA Antwerp. [Refers to pre-renovation. New hanging policy unknown as of today.]

Bruges is a very attractive medieval town center, with a very romantic feeling. But Belgium is loaded with lovely medieval town centers. I personally found the renovation of luxury single-story housing in the Beguinage area to be a big loss for that romantic feeling.

Bruges is a one-day wonder. Sure, there are few rare, early paintings
in Bruges. How about 50 major Peter Paul Rubens on view every day at
KMSKA Antwerp

LOL, Tim, Rubens is not a personal favorite so 50 of his works at once wouldn't do a thing for this girl! All those fleshy ladies are sad reminders of my own Rubenesque COVID waistline these days ("No more frites and mayo for YOU!") But different strokes keep travel forums healthy 'cuz we don't all enjoy the same things, eh?

We had 4 nights/3/5 days in Bruges, including a day trip to Ghent, and found plenty to do. For example, that modest Michelangelo that had a star turn in the Monuments Men? The bigger reason to visit the church it's in (Onze Lieve Vrouwekerk) is for the story behind the individuals in the tombs in front of the high altar. Greer, in case you're interested, here's my version of the story down a bit into this previous thread:

https://community.ricksteves.com/travel-forum/belgium/bruges

Add to that the interesting churches of Jeruzalemkapel (that one is a gotta-do), 14th-century floor tombs in Sint-Salvators, Heilig-Bloedbasiliek ( Basilica of Holy Blood) and a few others. The history behind St-Janshospitaal was fascinating and it has a nice collection of Memlings. We enjoyed the collection at Groeninge Museum very much, especially their Flemish Primitives. The Gruuthusemuseum was closed when we were there but is seeing positive reviews, and walking the city ramparts was fun on a sunny day; don't miss the windmills and old city gates. Add the squares, canals, city landmarks, lovely architecture - early mornings are a GREAT time for the camera - bridges, breweries, .... Lots to do, and a lot of interesting history to explore if you enjoy that sort of thing.

https://www.visitbruges.be/en

I won't disagree with Tim that Antwerp is also WELL worth a stay. We enjoyed our 3 nights there too, and will give it another go in the future. I just think there's more to Bruges than most visitors take time to explore, and the smaller size might appeal as a base.

Sorry, I would have to go with Ghent as another option. That gives you easy access to Bruges, Brussels, and Antwerp (all no more than an hour by direct train). Ghent itself is a wonderful city, plenty of restaurants, old architecture, and a really vibrant community not overwhelmed with the tourist crowds. I will add that I "skipped" Ghent on three or four trips to the area...focusing on Bruges and Brussels, however spent several nights there in November, and regretted that I had missed out all this time. You relly need to reconsider.

Brussels is the least interesting of the cities, a big, dirty, crowded town. The city center is worth a visit, but beyond the Grand Place is just a warren of tourist and waffle shops. Bruges is nice, again well worth a visit, touristy in an ok way, but as a base, puts you an extra hour each way to get to the other cities (for which you will be going through Ghent each way!)

For the Flanders Fields and Ypres, you will want a car for the day, both to ease getting there and back, but also to get to some of the more interesting sights.

We stayed 3 nights in Bruges and 2 in each Ghent and Antwerp. Our last night was in Brussels simply because it was closer to the airport in case there was a train strike. To us, other than the Grand Place there’s little else there. We used Quasimodo for the Flanders Field tour and got picked up at our hotel in Bruges. It was a full day tour and worth the money. Photos from that trip are on my website.

The Groeninge Art Museum rocks. It is so great I drop in every time I visit Bruges and the scenic bridge over the canal there is one of Bruges’ most photogenic spots.