Ceiling-mounted ‘cassette’ units are very popular in modern offices. Although they are slightly more expensive than wall units, ceiling ‘cassettes’ are almost entirely hidden within a suspended ceiling and are therefore more discreet and aesthetically pleasing; all that is visible is an almost-flush facia panel.
They also have the advantage of providing four-way airflow so they are ideal for large offices where multiple areas must receive balanced cooling. Some ceiling ‘cassette’ aircon units also have individually controlled louvers so that you direct the air around the office as required.
If you don’t have ‘false ceiling’ then you are better off using a wall-mounted system.