Antennas are devices that transmit or receive electromagnetic waves. Depending on how they transmit and receive electromagnetic waves, antennas can be classified into directional and omni (omnidirectional) antennas.
As the name implies, omni-directional antennas(ceiling mount antenna, outdoor fiberglass omni antenna and other customized antennas) receive and transmit signals in all directions. An omni antenna transmits/receives signals in such a way that, along one plane, the signals are sent out in all directions with equal strength while the strength of signal varies as you move in any plane perpendicular to that plane.
They are a good choice for most users as they provide consistent coverage over a broad area and can service multiple providers.
A directional antenna(indoor panel antenna, outdoor panel antenna and other customized antennas) is an antenna that transmits or receives signals most strongly in one direction. In order to transmit/receive a signal from a directional antenna, the transmitter and the receiver need to be pointed towards each other. When the directions are aligned, the receiver receives the best possible signal. For Directional antennas to be effective, they must be pointed in the direction of the cell tower.
How to choose the most suitable antenna for using? It depends on your individual situation. If you live in an area with weak cell phone signal, due to distance from cell towers, you will want to select a directional antenna. If you are a business that has weak signal for multiple providers, this may require purchasing multiple directional antennas and pointing each in a different direction to the corresponding cell tower. An omni-directional antenna may help, but it would likely not perform as well as a directional antenna in this circumstance.