Framelock (difficult to impossible to cut with a portable grinder; always on the bike; locks/unlocks in seconds - no fiddling).
Hiplok (to secure the bike to a fixed object. Framelocks do not secure the bike in place. The bike could be rolled away or put in a truck.)
[EDIT]
Perhaps the best deterrent is rim brakes. Nobody wants to be seen riding rim brakes.
[/EDIT]