Before installing the aerial, you need to check the distance from your TV to the transmitter. If the distance is in between 15 miles, you can install an internal digital aerial. If the distance in between 15 to 30 miles, an external digital aerial would be preferred. If the distance between your TV place to the transmitter is more than 30 miles, which is very rare. You need to install a satellite aerial.
Another important factor is the cost of the aerial. Different aerials vary in cost due to the difference in their properties specially range. If internal aerial can work good for your TV, do not install external digital aerial because its more expensive. If external digital aerial works for your TV than do not install satellite aerial because its more expensive.
Different companies are offering different packages for TV signals and aerials. Some of the companies are charging for the channels. Freeview aerials are offering free HD channels and standard channels. It is also a very important factor to consider.