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Definately the car engine.
Car engines are designed for more torque at lower rpms. Often small displacement car engines will be undersquare to help optimize low end torque. Parts are often heavier for more durability. Economy of scale means more development time for EFI maps. Example: Geo Metro's undersquare 1.0L engine makes 49-55hp at about 5000rpms (depends on exact model) and 55ft-lbs at 3300rpms.
Motorcycle engines are designed for peak power, and thus higher rpms. Often these will be oversquare to reduce stress on the crankshaft at high rpms and allow for larger/more valves. Extremely lightweight parts are used to allow for high rpms and durability is not as critical. Often won't have as much refinement in EFI mapping. Example: Kawasaki ZX10R's oversquare 1.0L motor makes ~210hp at 12500 and 83ft-lbs at 8700rpms.
(Note: these aren't quite apples to apples since the Geo is a 3cyl and the ZX10R is a 4cyl. But, there aren't many car and bike engines that the displacement matches up)
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