Either way. Depends. How is that for an answer!

Here is what I do.
If there is a lot of floating debris, I aim the jet towards the surface to encourage rotation towards the skimmer. If there is a lot of debris on the floor, I aim it downward but again towards the side to try to get it all in the center where it will be easier to vacuum it up.

You will soon learn what works best for your pool.

Welcome to the Pool Forum!