[TimelessFate]

First of all, tl;dr (Too long; didn't read)

Here is my opinion between the two.

Kicking will provide more force depending on how the robot does it. Just a regular kick, like we would do, can propel the ball pretty hard. It depends on where the kicking device stops too. We all know, when kicking a soccer ball, we can either get it up in the air or launch it across the ground. The problem I see with a kicking device is pulling the kicking device up into its resting position.

The punching method is a lot more simple and works well with the KISS method. A pneumatics piston would do the job easily. The problem I see with this is getting the piston to provide enough force to launch the ball and get it over the bumps on the field.