The answer to this question does depend slightly on your own personal preferences. On the market, most air conditioners will have a sound level of between 30 dBA to 70 dBA. The sound a human makes when breathing is somewhere around 10 dBA, so 30-70 would range from a normal conversation to a group of numerous people talking at the same time.
We would suggest looking for an AC unit with a sound level that sits somewhere between 20 dBA to 50 dBA. It’s important to remember that the decibel level your air conditioner makes will also depend on the mode you are using.