We lived in a now-ubiquitous boxy duplex for almost a decade. Shared-wall noise was never a problem, I was actually quite impressed at how good it was.
Things that WERE a problem though:
• Like a lot of these places, it was built by a small developer with not much experience, so the long-term build quality was suspect in some areas, and terrible in others (our balconies weren’t sloped properly, and the eavestroughs were under built, so we had drainage and water issues almost from the start). It mainly affected our side, but some issues affected the neighbours too…which of course can pose problems. Luckily our first neighbours were great so we solved these issues amicably. But then they moved and were replaced by new neighbours. Things went south (see below!).
• Our second neighbours were hippie hot-tub party people. The hot tub was placed adjacent to our bedroom window, so 2-3 times a week we went to sleep listening to them getting drunk and high, all to the lovely smell combo of weed and hot tub chemicals. Not the end of the world, but still.
• They also had 3 dogs, who daily used our side of the lawn as their toilet. Again, not the end of the world, but urge to kill rising.
• During Covid, they went to BC for a year and turned their place into an AirBnB rental…which eventually turned into a party house for teens (because they couldn’t go clubbing). It got crazy enough that the cops showed up almost every weekend for a month. This was basically the last straw.
So as you can see, the biggest issue with the duplex was not the property itself (although I didn’t want to be left holding the bag)…it was the fact that no matter how nice of a place you have, you’re never fully in control of your property because you can’t control who you’re sharing with. For you, it may not ever be an issue. For us, it turned into a bit of a nightmare scenario, so we made like a tree and got outta there.