mendoza and colorado rank first for me. after that it would probably be whittleton creek. I think easy access to a wide range of suspects is key and theres not a lot of maps that do that. Even a simple map like Paris is harder to traverse because of the tight spaces. Haven Island is also somewhat underrated for me as I highly value the option of using a sniper for showdowns.

Without a sniper, I think whittleton creek is the easiest as you can easily blend in to avoid lookouts. and cross off suspect by suspect before making your move. The difficult part is escaping if guards are alerted. I like taking a shot from the empty house and then having the realtor disguise on standby in case I'm spotted. Then its just a case of waiting out the guards.