It’s not easy to recommend where to stay. Much depends on the vibe if you like a place or not, what is hard to explain. Bruges, Ghent and Antwerp are as everybody knows all three historic places. The first has a small town feel, the last certainly the vibe of a world harbour, Ghent is (literally too) in between. Ghent and Antwerp are both university cities and more lively in the evening.
If you are looking for variation a stay in Bruges can really add to the experience. After the crowds are gone in the afternoon (it can be really busy there) is Bruges surprisingly quiet. And that’s the time most enjoy exploring the place. You can do this after sunset when the buildings are beautifully illuminated. The same for the two other cities too.
On the way to the Netherlands you can always hop off, store your luggage at the railway station in case you missed something during an earlier visit.
The Belgian coast with it’s concrete buildings is far from attractive. With the exception of a few places like De Haan. It’s well known for it’s Belle Epoque architecture. Albert Einstein stayed there a half year in 1933 before finally moving to Princeton. You can follow his foodsteps and the villa where he stayed is still to admire, but (being in private hands) only from the street. De Haan is easy to reach with the coastal tram from Ostend or Blankenberge. Both within less than 15 minutes with the train from Bruges.