My first answer would be: the one you will practice consistently. However, let’s discuss the five major families. Whether you choose to practice Chen, Yang, Sun, Wu, or Hao, you will still benefit in increased health, better balance and internal and external energy, as well as stress reduction. The essential principles are pretty much the same from family to family. However, each style has a different way of moving the feet. The hand shapes are different as well (some open, some closed, etc.)
Chen (around 17th century) is the oldest form and later styles derived many of their movements from the Chen style (or family). The stance is low and movements alternate between slow and graceful and quick and forceful. It is a fairly athletic form, emphasizing spiral force and requiring good coordination.
Yang (mid1800’s) is the most widely practiced style. The movements are more expansive and exaggerated but still slow, gentle, and graceful. It is a fairly adaptable style for most physical conditions.
Wu (early 1800s) postures lean forward and backward. Movements are slow but emphasis is on redirecting the incoming force. The stances are more compact than Yang and hand movements are interesting and lovely to watch.
Sun (mid to late 1800’s) postures are different from the other styles and the hand movements are flowing and circular. Steps are agile and often include a “follow step”. The stance is higher and movements are compact and fairly easy to learn.
Hao (early 1800’s) is the least popular style. Movements emphasize internal force and correct positioning. It has a strong focus on controlling the qi, is well rounded, and is not a beginners form.
Tai Chi is practiced in every corner of the world and there are many forms and modifications. If you are a beginner or have physical limitations, it is important to choose carefully. Keep in mind that there is no “perfect” form. You may choose one and stick with it or you may experiment to find the one that feels “right” for you. No matter which form you choose, enjoy the journey. And remember, it takes regular practice to reap the many physical and psychological benefits that Tai Chi has to offer. Repetition, repetition, repetition………………