My wife and I have looked into townhomes, and I have a fair bit of experience in renovating. Most wood framed townhomes are not very well insulated against percussive sounds. They will prevent normal voice levels from getting through, but hysterical screaming or kids shouting will get through. But, unless there are concrete floors and walls, the most annoying sounds to get through are what I call percussive sounds. Running up and down stairs, jumping from couch to floors (kids i'm thinking here), and low level sound frequencies. God help you if your neighbours have a home theatre set up. Sub woofers will carry through wood framed buildings like nothing. And if your neighbours kid is learning piano...life can get pretty painful.
If you really are interested in a place I would strongly suggest you talk to the neighbours and get their views. And ask in you can do a sound test. Get you wife/partner to wait in the a neighbours living room living room and go jump up and down and shout a bit. It may sound silly, but whose the fool to put hundreds of thousands of dollars into a poor investment.
We bought a house