In choosing the best adjustable dumbbells, you must consider many factors, including short-term and long-term goals, purchase price and the overall quality and longevity of the product. Weight training equipment can be very high quality, but there also are dumbbell sets that are so poorly constructed that the locking mechanisms fail over time and the weights are no longer secure. In other cases, the paint coating might wear off and the weights might become so rusty that you don't want to use them any longer. If the adjustable dumbbells will be used infrequently, these problems might never manifest themselves, but constant exercising and continually adjusting the weight might lead to eventual equipment failure.
The first consideration when choosing a set is to know how much weight you need. Some adjustable dumbbell sets have a maximum weight of only 25 pounds — or perhaps 10 kilograms, if they are metric dumbbells — whereas others can go as high as 100 pounds or perhaps 40 or 50 kilograms. When determining the amount of weight you need, keep in mind your future usage. A lighter set might suffice for now, but in six months or a year, after you have increased your strength, it might be inadequate. Generally speaking, the greater the amount of weight included and the higher the complexity of the set, the greater the price.
Another important aspect is the nature and venue for use of the dumbbells. A set of adjustable dumbbells is heavy to move and manipulate in its entirety. If the set is purchased for home use, a system that includes a stand for storage and easy access is indicated. A stand also would be useful because the weights are more comfortably obtained from a standing position. If you take the weights somewhere else to train, then an actual case or built-in framework for carrying the set would be more appropriate.
Adjustable dumbbells are designed so that you can easily add and remove weight to suit your needs or for different exercises. Some sets do this with a pin system, and others use a spin lock or other internal mechanisms. The pin and internal twist lock mechanisms are subject to possible damage if the weights are constantly dropped or mishandled, but they provide for a fast and convenient way to change the amount of weight.
Some adjustable dumbbells are round like the traditional weights found at most gyms, and others are square. These designs affect the feel and balance when using them and should be a factor to consider when you are choosing a set. Finally, the size and shape of the dumbbells also affect range of motion when exercising, and even the necessary space required to store the set when not in use.