Double lift??? A pass/shift???
First of all, there's no such thing as the most useful sleight. However, the most versatile, and this is debatable with certain people, is a palm.
Anyone who has studied, and I mean STUDIED card technique and theory from old books and manuscripts will understand that a palm is among, if not the, most versatile sleight with cards as well as the adaptation for other things such as coins and small objects.
The palm. A grip is not necessarily a sleight but is part of technique when executing legerdemain.
I can do just about anything other sleights can do with only a palm. Force, switch, change, control, etc.
|| sean ||