You have two questions:
1. What is the difference between two techniques?
2. How does a player chooses the best?
On the side-step: I believe the side step is very effective but you are committed earlier in the move than the sink action. With this you can wait for the defender to move. Perhaps the side step can be executed at more speed....
The grubber kick is used in situations where you are too close to chip, the risk is that the grubber is blocked. What I like about the grubber is that you can kick in such a manner that the ball makes a tumble action and almost certainly will make a big bounce upwards. Internationals never have to bent over to pick up a ball, it always bounces up at the right moment!
How to choose the best? There is very little time to make this decision! You will have to program the brains of the players. First, make sure the mechanics of the movement are done well, than at more pace to the exercise and more options - feedback on the selection is important. Your advantage is you have so much time with your team!
Please read up on this:
read the article by Jeff Hollier