First of all, in that situation ATC usually is not much help. The best they can really do for you is to clear the field and airspace between you and the field so you have options. If it is a REAL emergency (not a precautionary one) you are going to be busy flying and planning your return. We train controllers to just get everyone out of the way and acknowledge the emergency, and usually “Cleared to Land Any Runway, Winds XXX at XX” The hardest part was teaching the controllers not to distract the pilot with stupid questions like number of people and fuel on board, say intentions, etc while the pilot is in the middle of the emergency.