Many of us think that more is always better. In some cases, this is very true, but not always with an omni-directional antenna. The gain of an antenna (measured in dBi) is the ability to direct the radio frequency energy in a particular direction.
High gain antennas (10/8dBi) radiate in a narrow pattern for a longer distance and are great for flat terrain with few obstacles. However, if your antenna location is high, your signal may overshoot anything below you. If your antenna is low down, obstructions may block your signal.
Medium gain antennas (5.8 dBi) have a more rounded and broader pattern. These antennas work well around obstructions and are great for suburban areas. In addition, they would allow you to connect with hotspots that are both vertically and horizontally near you.
Low gain antennas (3 dBi) have a broad radiation pattern and are best for rugged terrain or a dense urban environment. Your signal is less likely to be blocked by obstacles such as buildings and hills tight to your location.