To decide the best location, one should analyze his or her requirements and purposes as the location would differ a lot. For instance, if you want to install an exhaust fan in your bathroom, then it's better that you install it on the ceiling as a wall-mounted exhaust fan wouldn’t be as efficient and effective as the ceiling exhaust fan would be. If you require an exhaust fan for your kitchen, even then you require a ceiling fan so that all the pollutants in a kitchen get eliminated in no time and in a hassle-free manner.    A wall-mounted fan might not give good results in a kitchen as the pollutants that get produced there, travel upwards and therefore can be best expelled through a ceiling duct exhaust fan rather than by a wall-mounted exhaust fan. If you need an exhaust for a room that is upstairs, even then you require a ceiling fan for good airflow.   If you require an exhaust fan for a conference room, you might want to place your exhaust fan on the exterior side of the wall so that it produces less noise in the room and doesn’t disturb the activity in there. Similarly, for a specific requirement, one has to decide a particular position and location to install an exhaust fan.