I agree Green Giant arborvitae are a good choice and can make quite a barrier in a short period of time. As they say, "good fences make good neighbors," so either an actual fence or hedge will really help. I've had very bad neighbors in the past and both times when I called the police, the behavior stopped but they got much nastier with me. Always awkward to live right next to someone who dislikes you so a barrier will help with having to see them all the time as well. Good luck.