I would pick the biewer because they dont go through such a transformation!
I just love the coloring of the biewer. Actually i didnt even know what one was until i read this thread... though when i was looking for my second yorkie, a lady was selling a biewer under "yorkie", and i remember thinking, "omg there is no way that dog can be a yorkie because of the white!" --but now thinking back, it must have been a biewer.
i am not a fan of any other type of small dog other than a maltese- but only if it is bred with a yorkie. So, i'm glad i found out about the biewer!
I suggest having one of both!