Oblivion Ring targeting an Aura
According to the rulings on this card's gatherer entry


  01/10/2008 If the exiled card is an Aura, that card's owner chooses what it will enchant as it comes back onto the battlefield. An Aura put onto the battlefield this way doesn't target anything, but the Aura's enchant ability restricts what it can be attached to. If the Aura can't legally be attached to anything, it remains exiled forever.


It would appear that option 2 in your question is the correct interpretation.