This is what dogbreedinfo.com has to say:
The Cairn Terrier is a spirited, hardy, restless little busybody - a big dog in a small dog's body. Alert, loyal, merry, lovable and mischievous. They are somewhat independent, but friendly. Females tend to be more independent than males and some breeders feel that males are more affectionate. They are very curious, fearless and bold. They are easily trained and like to do tricks. Naturally patient with children and very playful. Cairns adapt well to their new homes. They are sensitive, and need firm, but not harsh, training and discipline. Without attention and training, the Cairn can become destructive and/or bark excessively. Cairns like to dig searching for vermin, so it is not wise to leave them unsupervised in a landscaped yard! This breed can be a chaser and should not be left off its lead in an unsecured area. Never leave a Cairn tied out, as he may fight larger dogs to protect his turf, sometimes with tragic consequences. This dog will get enough exercise running around a small yard, but if you live in an apartment, it will need a daily walk or a romp in the park. Life Expectancy about 12-15 years. That shaggy "natural" looking coat actually takes quite a bit of maintenance and a neglected coat soon becomes a sorry, matted mess. Brush several times a week, being gentle with the soft undercoat. Once a month, bathe the dog and brush the coat while it dries. Trim around the eyes and ears with blunt-nosed scissors and clip the nails regularly. The Cairn sheds little to no hair. Do not over feed the Cairn for it tends to gain weight easily. Treats should be limited, even though the dog may be almost irresistible when begging. Cairns tend to be allergic to fleas.
Height: Dogs 10-13 inches (25-33 cm) Bitches 9-12 inches (23-30 cm)
Weight: Dogs 14-18 pounds (6-8 kg) Bitches 13-17 pounds (6-8 kg)
1) can be a bit dog aggressive
2)Best with older considerate children
3)Good with other pets (not dogs) if raised with them from puppyhood
4)Reserved / Aloof / Wary with strangers
West Highland White Terriers are described in the standard as being "possessed of no small amount of self-esteem with a varminty appearance." This game and hardy little Terrier is easy to train. They are fairly friendly toward strangers and get along well with behaved children. Westies may snap when irritated, but are not as willful as many of the other Terrier breeds. They are lively and extremely self-assured toward other dogs. Westies usually do not pick fights with other dogs, although some males are combative with other males. They may chase a cat for fun, but usually will not hurt it. Robust, friendly, cocky and spunky. Westies just love companionship. Despite its size, they make a very good watchdog. These little dogs are easy to travel with. The Westie likes to dig and bark. These dogs enjoy a regular walk or sessions of play in the park, but won't be too upset if they miss a day.Life Expectancy about 15 years or more.The harsh, straight, short-haired double coat is fairly easy to groom and sheds little to no hair. Simply brush regularly with a stiff bristle brush. Brushing should keep the coat clean, so bathe only when necessary. Trim around the ears and eyes with blunt-nosed scissors. The whole coat should be trimmed about every four months and stripped twice a year. Most are fairly healthy. Some are prone to chronic skin problems, Perthe's disease (hip problems), hernias, liver disease, and jawbone calcification.
Height: Dogs 10-12 inches (25-30cm.) Bitches 9-11 inches (23-28cm.)
Weight: Dogs 15-22 pounds (7-10kg.) Bitches 13-16 pounds (6-7kg.)
1)Friendly with other dogs
2)Good only when raised with children from puppyhood
3)Good with other pets (not dogs) if raised with them from puppyhood
4)Friendly with strangers
so by that Cairns seem to be a bit more higher demand (grooming, exercise and behavior wise). They both will dig a lot (typical terrier) and bark if bored (or just whenever they feel like it
). Westies are a bit larger. I'll see what I can find from other places, I've never owned one so I can't give you my personal experience by I'll help as best I can.
-Erin