There's really no reason to buy a dog at all when there are so many animals sat in shelters and potentially being put down because someone would rather pay for a pure breed or something.
Also, if you're asking 'shall I buy this dog cos it's cute' then the answer is NO, you are nowhere near responsible enough to care for a puppy... they cost a lot of money and take massive amounts of work to train and care for and you need to be fully committed otherwise you're risking basically abandoning the animal which will be hugely traumatic