[MikeE]

I agree with most of Ether's OP.
Catapult-like devices (i.e. those that start in contact with the ball and accelerate with it) should be more consistent than shooters relying on impulsive contact such as kickers or punching devices.
The trajectory of the latter depends on more variables than the former, for example ball air pressure and exact contact point.

Beyond that it depends at what level we measure consistency: shots from a single location or ability to shoot accurately from a larger area of the field (i.e. robot scoring consistency). In other words we can argue that there is a balance between consistency of the energy source (where springs & pneumatics win) vs controllability where motors have an edge.