|Depends on what you a trying to achieve. |
An Omni antenna is simply an antenna that receives or radiates in all directions. The opposite of a directional antenna. You can get hi-gain omnidirectional antennas but it depends on what you are connecting to .
CDMA antennas are also omnidirectional. Directional antennas are usually used in a static environment.
A directional antenna is not much use in a mobile environment as you will need to know which direction to point it. For a directional antenna you would be looking for a Yagi antenna.
omni- comb. form all. [Latin omnis all]