4th Ave is a huge, 4-6 lane divided road with lots of new, inexpensive apartment buildings that have been built in the last 5-10 years. It’s fine and convenient, but quite transient and not very charming. It’s close to park slope proper which is quite charming. All of the slope is nice and safe, relative to other parts of brooklyn. Avenues tend to be louder, yes, but it’ll be more building specific and location/window type etc will matter more. North slope is probably more convenient if closer to Atlantic terminal for subway access.