As far as I am concerned, it is my choice. If PAN doesn't give me what I want, I'll shout Mayday. An engine failure in a twin is an inconvenience rather than a dire emergency, but you will have to land at the "nearest suitable" (which us not necessarily the closest). What you are doing with your call is to let then know of your plight, reserve tracks, levels and resources due to your problem; things you are going to take disregard less of what ATC say. My experience of ATC in Europe is such that they are extremely accommodating to any aircraft with even minor faults that declaring any emergency status is pointless. They will give you want you need anyway. With one exception - LHR. To a diverting aircraft low on fuel "LHR are only diverting accepting aircraft with an emergency. Do you have an emergency?" "Not yet, but if you keep me on this heading I will be." Five minutes later "Mayday, mayday..."