Size
The Greater Swiss Mountain Dog is a little larger on average: about 51 kg (113 lb) as an adult, against 41 kg (90 lb) for the Bernese Mountain Dog.
Shedding
Their coats shed differently: the Bernese Mountain Dog sheds through the year, the Greater Swiss Mountain Dog moults most as the seasons change.
Grooming
The Bernese Mountain Dog needs more grooming, daily brushing, where the Greater Swiss Mountain Dog needs brushing a few times a week.
Temperament
They differ most on independence (Bernese Mountain Dog: keen to work with you; Greater Swiss Mountain Dog: cooperative, with its own ideas) and on sensitivity (Bernese Mountain Dog: average; Greater Swiss Mountain Dog: hardy, takes a busy home in its stride).
Alike
Both are rated the same on affection: a lap or leaning dog.