It depends on the guest and the circumstances, but I'd rather have them stay in a common area or a place specifically for guests. Why? A person's bedroom has their own "stuff" in it; clothes, toiletries, etc...you know, stuff that might be personal to the one who regularly sleeps there, so I say keep the short-term guest in a more appropriate short-term area.
Still, it would ultimately depend on the guest and the circumstances.