“admin_enqueue_scripts” hook or $_GET[‘page’]?

The advantage of using the value provided by WordPress in the hook variable is future compatibility with WordPress Versions and not having to worry about $_GET variable manipulation by way of the user or another WordPress plugin.

Checking the $_GET array works, but can be unreliable especially when other poorly coded plugins start messing with the $_GET array, because it is not a global constant and can be modified.