Size
The Finnish Spitz is much larger: about 15 kg (33 lb) as an adult, against 8.8 kg (19 lb) for the Shiba Inu.
Grooming
The Finnish Spitz needs more grooming, daily brushing, where the Shiba Inu needs a brush once a week.
Exercise
Plan for plenty of exercise with the Finnish Spitz, and a moderate amount with the Shiba Inu.
Temperament
They differ most on affection (Finnish Spitz: affectionate on its own terms; Shiba Inu: likes its own space) and on handler demand (Finnish Spitz: needs steady training; Shiba Inu: needs an experienced owner).
Alike
Both are rated the same on independence: decides for itself.