With the various breeds of Terrier's that are known and loved around the world today, each Terrier's physical Agility characteristics can vary quite considerably. From the extremely enthusiastic breeds to the more relaxed, docile types, it is possible to find the perfect dog in the Terrier breed to compete in Agility competitions.
Airedale Terrier's are widely regarded as the most agile type of Terrier. Extremely energetic and highly intelligent, the Airedale Terrier has been known to regularly win many Agility based competitions. However, regular obedience training from an early age is highly recommended (if not a necessity) as the Airedale Terrier is known to have a somewhat stubborn attitude. This doesn't mean that the Airedale Terrier takes a long time to train, but purely that they may require more formal and regular obedience training than other forms of dogs.
There aren't many Terrier's that are considered completely clumsy, inactive and therefore unable to enter Agility competitions. However, the Staffordshire Bull Terrier, for example, is one of the least agile dogs and whilst they are able to be trained to compete in Agility events, they are much more comfortable in a less formal, non-exercise specific environment.