You will usually hear people say not to install a mirror unless there's something worth reflecting. A blank wall wouldn't be worth reflecting. Consider a nice piece of art.

Photos of the rest of the room would help. In a guest room, I would think a mirror would be an appreciated addition by those who might stay there. Consider hanging artwork on the opposite wall, and that will be reflected in the mirror.

Mirror is essential in bedroom. I would go with round oversized one and wall art on opposite wall.

A full size mirror may be more practical than one above the dresser. If you are short of space, you can always attach one to the back of the door. I agree with a peice of art over the dresser.

oversized round one in a plain black frame would look very nice. Then put a big oval platter on the top of the cabinet where people can put their eyeglasses, cell phone, keys, etc.

I would not put a big piece of art on the wall opposit if the room is small and if when the bed is is fully open it practically touches the opposite wall.

Instead of art, consider a rack of hooks, and hang a bathrobe for your guests.

A guest room should always have a mirror. That's a perfect place for one.