In my youth, I had a female GSD and a female Papillion. They got along fine but the Papillion was older and very much in charge. Once I brought home a giant bone which the Papilllion could not even get her mouth around--she wedged it into a corner and didn't let the shepherd have any.
But it really depends on the dogs and the environment. I'd say to go with a reputable breeder and have a trainer lined up. My brother in law started having problems with his shepherd and his dachshunds when the shep reached adolescence.