Load all of the scripts asynchrously so they don’t block DOM construction while the browser fetches them, but make sure to include script 1 first in the HTML.
Load script 1 normally (without an async or defer) attribute and load scripts 2 and 3 with the defer attribute.
Load all 3 scripts with the defer attribute, making sure to include script 1 first in the HTML.
It doesn’t matter. The scripts can be executed in any order.