Which jet airliner types have had the fewest accidents per million departures?
All newly developed types have zero number of accidents, at least immediately before the maiden flight. 

Hence the actual safety of the type cannot be derived just from the number of the accidents. The number of flights flown must also be taken into consideration. For instance, Concorde used to be the absolutely safe (zero accidents) for many years (1969 - 2000), then it became comparable to other planes just because of the only crash of the type.

This source contains the table that includes the number of airliners operating, not just the number of accidents. It is very incomplete but looks like Boeing 777 and ERJ 135/145 may not be a bad choice while Boeing 737 'Classic' does not look equally good. The safety of this type has been discussed separately.