There are many well respected and reputable tennis companies that produce and sell quality ball machines, such as Wilson, Prince, and Lobster.

When buying a portable tennis ball machine, one of the first factors to take into consideration is the level of power the tennis ball machine will have, which is solely dependent on your skill level and level of progress. Most portable tennis ball machines will have a variety of power levels, however, some will be more accustomed to your needs that others.

You will also need to consider battery life and battery consumption, and look for portable ball machines that have the option of being plugged in to a power source as well.

Capacity is also another important factor to consider when buying a portable tennis ball machine. Different machines have different ball holding capacities, and so if you wish for a longer, less interrupted session you will need to choose a portable tennis ball machine that has a high ball capacity.

Another important feature in portable tennis ball machines is oscillation. Oscillation allows the portable tennis ball machine to shoot the ball at different angles, allowing your practice session to resemble game practice instead of shot practice, which can make a dramatic improvement on your game.

Overall, when buying portable tennis ball machines, you will need to map out your game beforehand, such as your age, skill level and power, so that you can choose a ball machine that suits your game and will benefit you the most.