Probably the
most difficult was the KC-135 with the wretched 'boom-drogue adapter'....
Particularly if you were flying a Q-fit F4 and hadn't had any dual or even a brief - just sent off on a Q scramble having been told "It's just another tanker"....
I still have a tape (and now a DVD clip!) of a certain Irish Wing Commander prodding in a VC10K.....against a kiwi A-4. It looked a lot less tricky then Art's Valiant vs. Sea Vixen experience!