Plane, from what I have heard ( friends, not personal experience )
the less experience you have the more technical the interview gets, some guys from small t/prop backgrounds have been asked 20.7 stuff .
there are at least 3 different guys that do the interview so no 2 interviews will be the same.
As usual it pays to know about : the A/C you fly inside out, Virgin, Virgin fleet, CAOs and CARs, CRM, etc.