Depends on the species you want to attract. Wrens like the shrubs and cover but a Bluebird would like a house on a fencepost (with predator protection) out in the open with clear views. I don't know that the hanging vs fixed would have an effect unless the hanging one was very prone to swinging. I could see excessive swinging (like on a weak branch or one so small it moves in each breeze) as being detrimental to the eggs.
