How to properly return a collection of unique_ptr

After changing my code to use unique pointers, I stumbled upon how to return a collection of objects to a client. In general, I want to pass objects as references or non-owning pointers. But if I have a collection of objects, I can't just return the reference to it.

As an example, I have a simple class with a collection of objects, which are all created once and not altered afterwards.

using ObjectUPtr = std::unique_ptr<Object>;
class MyClass
{
  public:
  const std::vector<Object*>& GetObjectsOldStyle() const
  {
    return mObjectsOldStyle;
  }

  const std::vector<VObjectUPtr>& GetObjectsNewStyleA() const
  {
    // I don't like that: The client should not see the unique_ptr ...
    return mObjectsNewStyle; 
  }

  std::vector<VObject*> GetObjectsNewStyleB() const
  {
    // Ok, but performance drops
    std::transform(...); // Transform the collection and return a copy
  }

  const std::vector<VObject*>& GetObjectsNewStyleC() const
  {
    // Ok, only copied once, but two variables per collection needed
    // Transform the collection and cache in a second vector<Object*>
    std::transform(...);
  }

  std::vector<Object*> mObjectsOldStyle;    // old-style owning pointers here
  std::vector<ObjectUPtr> mObjectsNewStyle; // how I want to do it today
}

Today, I usually prefer GetObjectsNewStyleB, but I wonder, if there is a more elegant and efficient way or a general best practice on how to return such collections.