Both are pretty high maintenance as far as coat is concerned, especially if you keep them in a long coat. Shih Tzu have a double coat, as opposed the the Maltese's single coat, but both require a fair amount of grooming to stay neat and tangle free. Shih Tzu will probably have seasonal shedding, like other double coated breeds.
As far as personality and temperament go, both are supposed to be friendly, outgoing dogs.
Talking with good breeders of both breeds will give you a better idea of their similarities and differences.