Which has more impact on site performance? Template overrides or hooks

The templates are, by definition, the mechanism to define how a certain woocommerce page would look, and child themes are, by definition, the way you change a behavior of a theme beyond what it allows for in the Admin UI.

Overriding the templates in a child theme is the best practice. (Bear in mind that this means you may have to come back and update the template when Woocommerce updates their templates.)

Also, changing the content in PHP is usually cheaper than letting the default PHP run then changing the content in the browser, because it duplicates work.