Long post, sorry - this post really struck me as I’m planning to go the other way and sell a semi I love to take on a bigger mortgage for a detached I almost certainly won’t like as much. Due to neighbour noise.
To boil it all down, you really need to consider how much noise could bother you, because it does vary from person to person, as well as the construction and layout of the property.
Like other posters, I’m no longer happy with terraced and semi-detached properties. Not because I expect silence - lived in mid-terraces before and loved it, despite hearing some neighbour noise - and would happily live in a flat if I had quiet neighbours, but because I’m now finding I can’t tolerate antisocial noise. My MH has been badly hit by poor sleep due to slamming fire doors from next door at all hours. A noise earplugs don’t help with btw. When I read threads on here about neighbours, I wonder what my problem is as so many people have much worse! Have also been to the council about previous occupants of the same house - which worries me sick when I think about disclosing it when we (try to) sell. Different noise (and other) issues then.
I think you need to consider what it would be like if you did have noisy neighbours. Are you pretty laidback? People have different tolerances for noises and the different noises they hate - I could better tolerate living under a flight path than yelling and whooping in the middle of the night, for example (previous neighbour in this house). Would you be happy to make sacrifices like moving bedrooms, etc.?
Then construction. How thick are the walls? What is the internal layout? I live in a Victorian semi with four floors - tall and thin, and few rooms don’t have the party wall, which conducts sound the entire height of the building. If someone slams the lounge door you can hear it quite clearly in the attic. Slam a bedroom door and I can feel it. Tv noises travel one floor. I realise now the wall is single brick, which just isn’t enough.
Soundproofing - we looked into this, but were put off for two reasons: losing inches in the rooms (self-explanatory) and not knowing how far to go. If you read about this at all, you soon realise that soundproofing a single wall is not considered sufficient if you really need to block sound. That needs work on floor, ceilings, etc. I didn’t want to spend so much money if it wasn’t necessary, but nor did I want to spend ££ on sou;dpriofing s wall to find it didn’t achieve very much. Pretty sure the booming door issue I have wouldn’t be solved with a one-wall, one-room solution. If you’re seriously thinking now that you might do this if there is a neighbour issue, I’d do some research and try to find people who’ve have different types fitted to find out what it has achieved for them.
Smells come through too. Weed and a really nasty meat smell in this case!
This isn’t to put you off. As I say, I was very happy in my previous places, all terraced and exposed to some noise. It’s being at the mercy of neighbours that is the problem as pps have said.