Size
The West Highland White Terrier is far larger: about 9.6 kg (21 lb) as an adult, against 3.5 kg (7.7 lb) for the Maltese.
Shedding
Their coats shed differently: the Maltese sheds through the year, the West Highland White Terrier holds loose hair until it is brushed or clipped out.
Grooming
The Maltese needs more grooming, daily brushing, where the West Highland White Terrier needs a brush once a week.
Exercise
Plan for a moderate amount of exercise with the West Highland White Terrier, and a modest amount with the Maltese.
Temperament
They differ most on sensitivity (Maltese: needs a calm, predictable home; West Highland White Terrier: hardy, takes a busy home in its stride) and on prey drive (Maltese: usually fine with small pets; West Highland White Terrier: likely to chase small pets).