In most cases that involve testing oxygen consumption or metabolic rate, choosing the best fitness testing equipment is going to involve some trade off between the accuracy of the measurement and the price of the equipment or the tests. For measures of physical capability, however, the test can often be performed with a treadmill, an ergometer, or another piece of exercise equipment. Many can also simply be done outside with a stopwatch or a timer.
Determining an individual's level of physical fitness may require very expensive fitness testing equipment, or it may not require any equipment at all, depending on what measure of fitness is being taken and whether an estimate of the results is acceptable or an exact number is required. For example, if you choose to measure fitness based on body fat percentage and VO2 max, or the amount of oxygen the body can use during intense exercise, you have several options. You could choose to use body fat calipers or a hand-held bioelectric impedance device at home and have the person being tested perform a physical test that provides an estimate of VO2 max, such as a shuttle run test. Other possibilities are to have the tests done at a gym or doctor's office with their more expensive, high-tech fitness testing equipment, or you could buy this equipment for your own use.
In order to determine the best fitness testing equipment for your needs, you should first figure out what aspects of fitness you will be testing, the individual or group of individuals you will be testing, and how frequently you plan on doing the tests. If you are opening up a health club or training to become a personal trainer, it might be worth the money to purchase your own VO2 max and resting metabolic rate testing equipment because you will be using these machines frequently on a large number of people, many of whom you can charge for the tests to make up for the cost of the equipment. On the other hand, if you simply want to test your body fat percentage every now and then to track your weight loss progress, it would be much more cost effective to have the tests done for you at a gym or doctor's office or to buy an inexpensive set of body fat calipers or a hand-held bioelectric impedance device.
Regardless of what type of fitness testing equipment you decide to use, you still need to determine the equipment's quality before you purchase anything. Ask gym owners and personal trainers for recommendations on the best, most reliable fitness testing machines. Reading reviews online and ensuring a decent return policy should be adequate before buying the less expensive options.