Warm Air Rises unless otherwise moved.
Way 1 (my pick): Warm air is either expelled out the back or up top
Way 2: Cooler Air is brought it, mixed with the warm air inside and spread out the top. This leaves the hot air inside the machine longer, and leaves it vulnerable to overheating if the outside temperature is too high,
Way 3: Hot air is expelled downward, where it simply rises back up, reheating the machine.
Way 4: Rising hot air is forced downward, creating a core of heat at the center of the machine. This also leaves the machine culnerable to overheating by hot ambient temeprature.
Way 5: Same as Way 3, not to mention air coming out the front of the machine could be annoying.
Way 6: Same as 3 and 4
Way 7: A core of hot air is pushed downward, where it reheats the machine.